Why Don’t I Feel Sleepy If I Have Insomnia? The Science of Fatigue vs. Sleepiness

Quick Summary

• A large study of over 1,300 people found that patients with insomnia report almost no more daytime sleepiness than good sleepers, despite feeling exhausted (Fasiello et al., 2024).

• Sleepiness (the urge to fall asleep) and fatigue (the feeling of exhaustion) are separate things: statistically, they barely relate to each other. Only fatigue tracks with how bad someone’s insomnia actually is.

• A round-the-clock “wired but tired” brain state called hyperarousal is the leading explanation for why insomnia doesn’t produce daytime sleepiness the way sleep deprivation normally would (Riemann et al., 2010).

• Effective insomnia treatment (CBT-I) significantly improves fatigue and daily functioning, but daytime sleepiness actually ticks up slightly, a sign the treatment is rebuilding healthy sleep pressure (Maurer et al., 2021).

If I Have Insomnia, Why Don’t I Feel Sleepy?

For a typical sleeper, if you haven’t slept well, feeling sleepier the next day is a normal physiological response to sleep loss.

Given that chronic insomnia is a disorder of persistent difficulty sleeping, it makes sense that both major diagnostic manuals list daytime sleepiness as one of insomnia’s defining daytime consequences (American Academy of Sleep Medicine, 2014; American Psychiatric Association, 2013).

But is this actually accurate? Are people with diagnosed insomnia actually sleepy?

Surprisingly, the leading scientific model of insomnia does not predict daytime sleepiness for those with chronic insomnia. Instead, the model predicts almost the opposite effect on sleepiness for those with insomnia. The hyperarousal model holds that chronic insomnia is driven by a nervous system stuck in high alert for the full 24 hours, not just at bedtime (Riemann et al., 2010). This results in a lack of sleepiness both day and night.

So the diagnostic manuals and the leading model of insomnia are at odds. Is sleepiness actually a symptom of insomnia?

A team of Italian and Greek researchers set out to settle this question directly, comparing Epworth Sleepiness Scale scores across more than 1,300 people: patients with insomnia, healthy sleepers, and patients with disorders where excessive sleepiness is the defining feature (Fasiello et al., 2024).

Before getting to what they found, it helps to clarify something we usually collapse into a single word: tired. Tired is a synonym for both sleepiness and fatigue. But are these two the same thing?

What’s the Difference Between Sleepiness and Fatigue?

Sleepiness and fatigue are distinct states with different causes, but English gives us one everyday word that can cover both: tired. This causes confusion because “feeling tired” doesn’t distinguish whether someone is sleepy or whether they are fatigued.

Sleepiness is the physical drive to fall asleep, showing up as drowsiness, and an inability to stay awake (Johns, 1998).
Fatigue is a feeling of exhaustion and depleted energy that isn’t necessarily accompanied by any urge to nod off (Shen et al., 2006).

Think of it this way: sleepiness is what you feel on a quiet Sunday afternoon on the couch, sun streaming into the room, and you can’t stop nodding off. Fatigue is what you feel after a long, draining day at work: worn out, but too wired to actually drift off.

For those with chronic insomnia, this distinction matters. Why? Because insomnia’s fatigue tends to be chronic, has a real impact on daily life, and isn’t fixed by rest (Shen et al., 2006).

So does insomnia produce sleepiness or fatigue?

Does Insomnia Result In Sleepiness Or Fatigue? How Did Researchers Test This?

Researchers compared scores on a commonly used scale that assesses sleepiness, the Epworth Sleepiness Scale (ESS), across five carefully chosen groups:

• 671 patients diagnosed with insomnia disorder by a sleep medicine specialist,

• 105 healthy sleepers, and

• 602 patients with disorders defined by real excessive daytime sleepiness,

  • 545 with obstructive sleep apnea)

  • 30 with narcolepsy type 1, and

  • 27 with idiopathic hypersomnia (Fasiello et al., 2024).

To be included in the healthy-sleeper group a person had to scroe 10 or below on the ESS,  alongside no insomnia symptoms and healthy sleep quality more broadly.

The ESS itself is a brief questionnaire rating how likely you are to doze off in eight everyday situations, like sitting and reading or riding as a passenger in a car. ESS scores run from 0 to 24, and above 10 suggests clinically excessive sleepiness (Johns, 2000).

The insomnia group also completed the Insomnia Severity Index (ISI), which scores how severe and disruptive the disorder is, plus a separate mood questionnaire measuring fatigue.

A subset of 435 of the insomnia patients then went a step further, completing a structured, seven-session course of CBT-I, which let the researchers track what happened to sleepiness once the insomnia was actually treated.

So, with the groups and the measures in place, how did the numbers actually stack up?

How Sleepy Are People With Insomnia, Really?

Fasiello et al’s research revealed people with insomnia are almost exactly as sleepy as healthy sleepers, and much less sleepy than people with disorders that genuinely cause excessive daytime sleepiness.

After accounting for age and sex differences between the groups, the results looked like this (Fasiello et al., 2024):

Group	Average ESS score (0–24)	% with excessive sleepiness (ESS > 10)
Insomnia disorder	4.8	9%
Healthy sleepers	5.3	0%*
Obstructive sleep apnea	10.0	46%
Narcolepsy type 1	16.3	89%
Idiopathic hypersomnia	13.8	97%

*By design: an ESS ≤10 was a requirement for joining the healthy-sleeper group.

So people with insomnia actually scored slightly lower on sleepiness than the healthy-sleeper group. Further, the gap between insomnia and the three sleepiness-defined disorders was statistically significant, p < 0.001 in every single comparison - basically, the differences are unlikely to be by chance.

Fewer than 1 in 10 people with insomnia crossed the threshold for clinically excessive sleepiness, compared with roughly 9 in 10 people with narcolepsy or idiopathic hypersomnia.

This suggests that for a symptom the diagnostic manuals list as a core daytime consequence of insomnia, there may be an unusually weak link.

These are still self-reported scores, though. Would a more objective, lab-based test back this up, or tell a different story entirely?

Does Objective Testing Support Insomnia Patients Not Being Sleepy?

Objective testing supports and arguably strengthens the case that those with chronic insomnia are not overly sleepy. The multiple sleep latency test (MSLT) is a lab-based measure that times exactly how long it takes someone to fall asleep during a series of scheduled daytime naps. Basically, the test is just a research volunteer lying down for a nap every couple of hours while a machine simply times how long it takes them to drift off.

Studies using the MSLT in people with insomnia have consistently found either no meaningful difference from healthy sleepers, or that people with insomnia actually take longer to fall asleep during the day (Bonnet & Arand, 1995; Edinger et al., 2021).

So not only do people with insomnia report less daytime sleepiness on questionnaires, objective testing backs this up. Many people with insomnia find it harder to doze off during a nap opportunity than someone who slept perfectly the night before.

So if sleepiness isn’t the daytime cost of insomnia, what is?

If Sleepiness Isn’t the Problem In Insomnia, What Explains the Exhaustion?

The exhaustion of insomnia is due to fatigue. Fasiello et al’s results found that fatigue is what actually tracks with how severe someone’s insomnia is; sleepiness essentially doesn’t.

Among the 671 people with insomnia, ESS scores showed essentially no relationship with either overall insomnia severity (r = -0.023, close to zero) or its daytime impact on work, mood, and concentration (r = 0.033, also close to zero).

Fatigue, measured with a separate mood questionnaire, told a completely different story: fatigue correlated meaningfully with both insomnia severity (r = 0.463) and daytime impact (r = 0.491) (Fasiello et al., 2024).

In other words, insomnia doesn’t leave you drowsy; it leaves you drained. That single distinction may be exactly why so many people with chronic insomnia describe feeling “tired but wired”, desperate for rest, yet unable to relax enough to actually nap.

So why would a body that struggled to sleep during the night, fail to produce any sleepiness during the day?

Why Don’t People With Insomnia Feel Sleepy?

The lack of sleepiness in insomnia is thought to involve hyperarousal: a state of heightened mental and physical alertness that persists around the clock, not just at bedtime (Riemann et al., 2010). The same overactive nervous system that keeps someone staring at the ceiling at 2am appears to also be what keeps them from feeling drowsy at 2pm.

Researchers have found physical evidence for this in the form of faster brainwave activity in people with insomnia, both during sleep (Spiegelhalder et al., 2012) and while awake (Colombo et al., 2016).

Hyperarousal acts a bit like a low hum of background alertness that never fully switches off. Sleepiness does still show up in insomnia sometimes, typically early on, when someone is genuinely sleep-deprived, or when insomnia coexists with depression or periodic limb movement disorder, a condition causing involuntary leg jerks during sleep (Roth & Roehrs, 2003).

But in longstanding or chronic insomnia, hyperarousal appears to actively override the biological signals that would otherwise produce daytime sleepiness.

Does that same override affect how clearly people with insomnia can think?

Does Insomnia Affect Your Thinking During the Day?

Insomnia is linked to plenty of daytime cognitive complaints, but the objective evidence for real impairment is surprisingly thin. And what impairment does exist is related to fatigue, not sleepiness.

A meta-analysis pooling many smaller studies found only a small-to-moderate drop in performance on tests of thinking and memory in people with insomnia (Fortier-Brochu et al., 2012).

There’s also a notable gap between how impaired people with insomnia feel and how they actually perform. Research has repeatedly found a mismatch between self-reported concentration problems and objective test scores (Orff et al., 2007).

This gap shows up in treatment too: a digital CBT-I trial found that patients’ subjective ratings of their own thinking improved substantially after treatment, while their objective test scores barely moved (Kyle et al., 2020).

That mismatch suggests CBT-I, the recommended first-line treatment for insomnia, may work partly by easing how impaired insomnia feels, even where objective performance shifts far less.

Given that, what actually happens to sleepiness itself once insomnia is properly treated?

Does Treating Insomnia With CBT-I Decrease Or Increase Daytime Sleepiness?

Treating insomnia with CBT-I doesn’t reduce daytime sleepiness; instead sleepiness rises slightly as everything else, including fatigue, gets better . Among the 435 patients who completed CBT-I, insomnia severity nearly halved, dropping from 16.6 (in the moderate range) down to 9.1 (just into the mild “subthreshold” band).

Fatigue dropped substantially too, from 8.1 to 5.5.

ESS sleepiness scores, though, crept upward from 4.9 to 5.4, a small increase, but a statistically real one (Fasiello et al., 2024).

That should be reassuring for those with chronic insomnia. A core technique in CBT-I is time-in-bed restriction - deliberately limiting time in bed to rebuild a stronger natural sleep drive (Miller et al., 2013).

Earlier studies had already flagged that time-in-bed restriction can temporarily raise daytime sleepiness (Cheng et al., 2020; Kyle et al., 2014). A more recent trial showed why: during time-in-bed restriction, sleepiness rises while alertness falls, but sleep itself deepens. Patients reach deep, slow-wave sleep faster and show clearer signs of deeper, more restorative sleep, and by 12 weeks the sleepiness effect reverses entirely (Maurer et al., 2021).

In effect, CBT-I restores the body’s natural sleep-regulation machinery (Cervena et al., 2004), and a little extra daytime sleepiness along the way is a sign that machinery switching back on.

CBT-I is the recommended first-line treatment for insomnia; see how CBT-I compares to sleep medication for more on that broader choice.

But could medication itself cause a version of this sleepiness, just for entirely different reasons?

Could My Sleep Medication Be Causing My Daytime Sleepiness?

While those with insomnia are typically not sleepy during the day, if you do experience daytime sleepiness it is possible that a sleep medication can be a separate cause of daytime sleepiness, but through a completely different route than the insomnia itself.

Benzodiazepines, a class of sedating medication sometimes prescribed for insomnia, are effective partly because of that same sedation. But benzodiazepines are also linked to grogginess after waking, next-day sleepiness, fatigue, and memory difficulties (Holbrook et al., 2000).

A newer drug class, dual orexin receptor antagonists (DORAs), works differently again, blocking orexin, a brain chemical that promotes wakefulness. This means daytime sleepiness is their most common side effect (Rhyne & Anderson, 2015). That said, large phase 3 trials of one such medication, daridorexant, found excessive daytime sleepiness in under 1% of patients (Mignot et al., 2022).

But separating medication side effects from the insomnia itself matters for anyone genuinely trying to make sense of their own insomnia symptoms.

So what does all this mean for how insomnia actually gets diagnosed?

What Does This Mean for How Insomnia Is Diagnosed?

This research means daytime sleepiness may be the wrong symptom to look for when diagnosing insomnia, even though current diagnostic manuals still list it as a core daytime consequence of insomnia (American Academy of Sleep Medicine, 2014; American Psychiatric Association, 2013).

Fasiello et al argue this could actively mislead clinical practice: if someone with insomnia symptoms also reports genuine, strong daytime sleepiness, that combination more likely points to something happening alongside the insomnia, such as sleep apnea, periodic limb movement disorder, or depression, rather than being explained by the insomnia itself (Fasiello et al., 2024).

For anyone living with insomnia, that distinction is quietly validating. It confirms what many patients already sense deep down: the problem was never that they can’t stay awake. The real problem is that they can’t switch off.

Where To From Here?

If this article describes your experience (constantly worn out, but unable to nap or truly relax), that exhaustion is real, and it’s a well-documented feature of insomnia. The hyperarousal driving this pattern is well understood, and it responds to treatment.

Because generic sleep hygiene advice and healthy sleep tips are unlikely to shift a nervous system stuck in overdrive, addressing insomnia and it’s accompanying fatigue calls for a more targeted approach. Working with a Behavioral Sleep Medicine specialist means a structured, individualised CBT-I programme built around your specific patterns, rather than one-size-fits-all tips. A sleep psychologist can tailor a plan that directly targets the hyperarousal and sleep-pressure imbalances described here, helping your body relearn how to power down, not just at night, but across the whole day.

Frequently Asked Questions About Insomnia, Sleepiness, Fatigue

Q1: Why don’t I feel sleepy even though I have insomnia?

A1: Because insomnia rarely causes genuine daytime sleepiness: a large study of over 1,300 people found that patients with insomnia scored almost identically to healthy sleepers on a standard sleepiness questionnaire, and far below people with disorders like sleep apnea or narcolepsy (Fasiello et al., 2024). The leading explanation is hyperarousal: a nervous system stuck in high alert around the clock, which suppresses the normal biological pull toward daytime sleep (Riemann et al., 2010).

Q2: What’s the difference between feeling sleepy and feeling fatigued?

A2:  Sleepiness is the physical drive to fall asleep: drowsiness, foggy attention, and the urge to nod off (Johns, 1998). Fatigue is a feeling of exhaustion and depleted energy that doesn’t come with any urge to sleep (Shen et al., 2006). English uses one word, “tired,” for both, which is why the two get confused so often.

Q3: Is fatigue a symptom of insomnia?

A3:  Yes: fatigue, not sleepiness, is the daytime symptom that actually tracks with insomnia severity. In a large insomnia sample, fatigue scores correlated meaningfully with both insomnia severity (r = 0.463) and its daytime impact (r = 0.491), while sleepiness scores showed essentially no relationship with either insomnia severity nor daytime impact (r = -0.023 and r = 0.033) (Fasiello et al., 2024).

Q4: What does “tired but wired” mean, and is it a real thing?

A4: Yes. “Tired but wired” describes the common insomnia experience of feeling drained and desperate for sleep, while still being too mentally and physically activated to relax enough to actually sleep or nap. It matches the hyperarousal model of insomnia, in which the same nervous system overactivity that disrupts sleep at night also blocks the daytime sleepiness that broken sleep would normally cause (Riemann et al., 2010).

Q5: Does CBT-I make you sleepier before it makes you better?

A5: It can, temporarily, and that’s expected. In one study, daytime sleepiness scores rose slightly during a course of CBT-I even as insomnia severity and fatigue both improved substantially (Fasiello et al., 2024). This is linked to time-in-bed restriction, a core CBT-I technique that rebuilds natural sleep pressure: the mild sleepiness increase tends to reverse within about 12 weeks as sleep consolidates (Maurer et al., 2021).

Q6: Should I be worried if I have insomnia and I am also very sleepy during the day?

A6: It’s worth checking with a specialist. Genuine excessive daytime sleepiness isn’t typical of chronic insomnia on its own. Dozing off in meetings, in front of the television, or while driving more often points to something happening alongside the insomnia, such as sleep apnea, periodic limb movement disorder, or depression (Roth & Roehrs, 2003; Fasiello et al., 2024).

Q7: Can sleep medication cause daytime sleepiness?

A7: Yes, through a different route than the insomnia itself. Benzodiazepines are linked to grogginess, next-day sleepiness, fatigue, and memory difficulties (Holbrook et al., 2000). Newer medications called dual orexin receptor antagonists (DORAs) block a wakefulness chemical called orexin, and daytime sleepiness is their most common side effect (Rhyne & Anderson, 2015), though this varies by drug; one newer option, daridorexant, reported daytime sleepiness in under 1% of patients (Mignot et al., 2022).

Q8: What is the Epworth Sleepiness Scale?

A8: The Epworth Sleepiness Scale (ESS) is a short questionnaire that rates how likely you are to doze off in eight everyday situations, such as sitting and reading or riding as a passenger in a car. Scores range from 0 to 24, with scores above 10 suggesting clinically excessive daytime sleepiness (Johns, 2000).

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Written By Dan Ford, DBSM, Sleep Psychologist

Published By The Better Sleep Clinic