Why Can't I Sleep? Common Causes of Insomnia

You're exhausted, you climb into bed, and then your brain switches on. Or you fall asleep fine but jolt awake at 3 a.m. and stare at the ceiling. If this sounds familiar, you're not broken and you're not alone. Insomnia usually has a specific, fixable cause, sometimes several stacked on top of each other. Here's how to figure out what's actually keeping you up, and what to do about it.

Key takeaways

Most sleep problems trace back to a handful of common causes: stress and a racing mind, poor sleep habits, caffeine and alcohol, evening screens, and an uncomfortable bedroom.
Acute insomnia is short-term and usually tied to a clear trigger. Chronic insomnia means trouble sleeping at least 3 nights a week for 3 months or more.
Fixing the underlying cause matters more than chasing symptoms. Supplements can help short term, but they don't replace better habits.
Loud snoring, gasping, or heavy daytime sleepiness can signal a medical problem like sleep apnea. See a doctor.

Acute vs. chronic insomnia

Before hunting for causes, it helps to know which kind of insomnia you're dealing with, because they call for different responses.

Acute (short-term) insomnia lasts days or a few weeks and usually has an obvious trigger: a stressful deadline, jet lag, grief, illness, or a big life change. It typically resolves on its own once the trigger passes.

Chronic insomnia is defined as difficulty falling or staying asleep at least 3 nights per week for 3 months or longer, despite having enough opportunity to sleep. This is the type worth taking to a doctor, because it's more likely to have a deeper cause and more likely to feed on itself, worrying about sleep makes sleep harder.

The most common causes of insomnia

Stress, anxiety, and a racing mind

This is the number one culprit. When you're stressed, your body stays in “alert” mode, pumping out cortisol and adrenaline that are the exact opposite of what you need to drift off. Money, work, relationships, health, the mind loves to replay them the second your head hits the pillow. Anxiety and depression are especially tightly linked to insomnia, and the relationship runs both ways.

Poor sleep habits and an irregular schedule

Going to bed and waking at wildly different times, sleeping in on weekends, or using your bed for scrolling and working all confuse your body clock. Your brain thrives on a consistent rhythm. Break it often enough and your natural sleep signal weakens. Our guide to how to sleep better naturally walks through rebuilding that rhythm step by step.

Caffeine, nicotine, and alcohol

Caffeine has a half-life of around five to six hours, so an afternoon coffee can still be in your system at bedtime. Nicotine is a stimulant too. Alcohol is the sneaky one: it knocks you out quickly but fragments the second half of the night, which is why a nightcap so often leads to 3 a.m. wakeups.

Screens and evening light

Bright light, especially the blue-toned light from phones, tablets, and TVs, suppresses melatonin, the hormone that tells your body it's time to sleep. Scrolling in bed also keeps your mind engaged when it should be winding down. Dimming lights and putting screens away an hour before bed is one of the highest-impact changes you can make.

Napping

A long or late-afternoon nap eats into your “sleep pressure,” the natural drive to sleep that builds up across the day. If you nap and then can't fall asleep at night, the nap may be the problem. If you must nap, keep it under 20 minutes and early.

An uncomfortable or warm bedroom

Your body needs to cool down to fall asleep. A room that's too warm, too bright, or too noisy fights that process. A worn-out mattress or pillow, or a partner who snores, can quietly wreck your sleep without you connecting the dots.

Medications

Plenty of common medications interfere with sleep, including some antidepressants, blood pressure drugs (beta blockers), corticosteroids, decongestants, and stimulants for ADHD. If your sleep trouble started right after a new prescription, that's a strong clue worth raising with your doctor.

Hormonal shifts and aging

Sleep changes across the lifespan. Perimenopause and menopause bring night sweats and hormonal swings that disrupt sleep for many women. As we age, sleep naturally becomes lighter and more easily interrupted, which is normal even if it's frustrating.

Pain and physical discomfort

Chronic pain from arthritis, back problems, headaches, or injury makes it hard to get comfortable and easy to wake. Pain and poor sleep amplify each other, so addressing one often helps the other.

When it's a medical issue

Sometimes insomnia is a symptom of an underlying condition rather than a habit problem. It matters to recognize the difference, because no amount of sleep hygiene will fix a medical cause.

Signs your sleep problem is medical

Some conditions need proper diagnosis and treatment, not just better habits:

Sleep apnea, marked by loud snoring, gasping or choking in your sleep, and heavy daytime sleepiness. Often noticed by a partner before you notice it yourself.
Restless legs syndrome, an uncomfortable urge to move your legs at night.
Thyroid problems, an overactive thyroid can cause insomnia.
Depression and anxiety disorders, both strongly linked to disrupted sleep.
GERD (acid reflux), which flares when you lie down. If any of these fit, talk to a doctor. Treating the root condition is what actually fixes the sleep.

What to do about it

Start by matching the fix to the cause. If caffeine is the issue, cut it earlier. If screens are the issue, set a wind-down routine. If stress is the issue, build in time to decompress before bed. The point is to address the cause, not just paper over the symptoms.

For techniques you can use tonight, our guide on how to fall asleep fast covers breathing methods and simple mental tricks. For a longer-term reset of your routine and environment, see how to sleep better naturally.

Supplements like melatonin, magnesium, and calming herbs can help take the edge off, especially in the short term or during a rough stretch. They work best alongside good habits, not instead of them. If you want to know which ones are actually backed by evidence, we break it down in our guide to the best sleep supplements. You can also browse everything in our sleep hub.

When to see a doctor

See a healthcare professional if your insomnia is chronic (3+ nights a week for 3+ months), if it's wrecking your daytime functioning, or if you notice signs of sleep apnea like loud snoring, gasping, or overwhelming daytime sleepiness. This article is general information, not medical advice.

Frequently Asked Questions

Why can't I sleep even when I'm exhausted?

Usually because your mind or body is still in an alert state. Stress and anxiety keep cortisol high, and evening light, caffeine, or a late nap can override your natural sleep drive even when you feel tired. The fatigue is real, but your nervous system hasn't switched off.

What is the difference between acute and chronic insomnia?

Acute insomnia is short-term, usually days to a few weeks, and tied to a clear trigger like stress or travel. Chronic insomnia means trouble sleeping at least 3 nights a week for 3 months or more, and it's the type worth taking to a doctor.

Can supplements fix my insomnia?

They can help, but mostly short term. Melatonin, magnesium, and calming herbs may take the edge off a rough patch, but they don't replace addressing the underlying cause, whether that's stress, caffeine, screens, or a medical condition.

When should I worry about not sleeping?

See a doctor if your insomnia is chronic, if it's seriously affecting your daytime life, or if you show signs of sleep apnea such as loud snoring, gasping in your sleep, or heavy daytime sleepiness. These point to a medical cause that needs proper treatment.