We include products we think are useful for our readers. If you buy through links on this page, we may earn a small commission. Here’s our process.

Some days — no matter how much coffee you consume — it’s a struggle to keep your eyes open, let alone complete the tasks you need to do at the office or home.

Yet all too often, when you finally climb into bed, you find yourself wide awake.

It’s frustrating. What the heck is going on?

Before you reach for those sleeping pills, discover all the things that could cause you to be tired all day but awake at night. Once you identify what might be going on, you can take action to support better sleep.

The circadian rhythm is like an internal timekeeper for everything our bodies do in a 24-hour period, explains sleep specialist W. Christopher Winter, MD, author of “The Sleep Solution: Why Your Sleep Is Broken and How To Fix It.”

This system uses light, dark, and our biological clock to regulate body temperature, metabolism, hormones (including melatonin), and sleep.

The body’s master clock is called the suprachiasmatic nucleus (SCN). Located in the brain, the SCN controls melatonin production. This hormone helps regulate sleep.

During the day when it’s light outside, melatonin levels remain low. Later in the day as it begins to grow darker, our bodies produce more melatonin, with levels peaking between 2 and 4 a.m. before falling again.

Our bodies are best primed to fall asleep about 2 hours after melatonin levels start to rise.

Everybody has their own circadian rhythm, Winter explains, which to some extent is genetic. So, unlike what your parents told you when you were a kid, there’s no reason you “need” to go to bed at a certain time.

“I don’t care what someone’s schedule is, as long as it feels right for them and is healthy,” Winter says.

However, if you’re tired but can’t sleep, your circadian rhythm may be off.

This could be a sign of delayed sleep phase syndrome. This occurs when you fall asleep 2 or more hours later than what’s considered “normal” (10 p.m. to 12 a.m.), making it difficult to wake up in the morning for school or work.

It often affects young people more — between 7 and 16 percent — but also occurs in about 10 percent of people with chronic insomnia.

Many people use the words “tired,” “sleepy,” and “fatigued” interchangeably, but there’s a subtle difference, says Winter.

At the end of a marathon, you feel fatigued — you likely don’t have the energy or motivation to run another marathon and perhaps not even walk the distance to your car. But you’re not sleepy — you wouldn’t doze off laying on the grass beyond the finish line. Rather, being sleepy is when you can barely keep yourself awake, Winter says.

Most of what affects your sleep happens when it’s still light. Learn healthy habits for superior shut-eye in our 12-day Clean Up Your Sleep Challenge.

If you’re tired but can’t sleep once the sun sets, it could be a sign of delayed sleep phase disorder. If not that, it could be something else or a combination of things.

Below are some reasons why you might constantly be tired, especially during the day.

1. Napping

Naps aren’t inherently bad. In fact, napping has several health benefits. However, the wrong nap strategy can keep you up when you should be getting deeper Zzz’s.

suggests that long naps and napping later in the afternoon can cause you to take longer to fall asleep at night, sleep poorly, and wake up more during the night.

Winter recommends keeping naps 20–30 minutes long, and napping at the same time every day so your body can anticipate it.

2. Anxiety

A racing mind isn’t conducive to peacefully nodding off.

No wonder sleep disturbance is a diagnostic symptom for some anxiety disorders, which older research says 24 to 36 percent

of people with insomnia also have.

Anxiety also leads to increased arousal and alertness, which can delay sleep even further.

Insomnia, narcolepsy, sleep disordered breathing, and restless legs syndrome were all reported.

The relationship between sleep issues and depression is complicated. It appears to disrupt circadian rhythms.

Inflammation, changes in brain chemicals, genetic factors, and more may all affect the sleep-depression relationship.

4. Caffeine

Maybe it’s time to reconsider that afternoon latte or energy drink.

On average, caffeine has a half-life of 5 hours. It may be no surprise, then, that research suggests that even 200 milligrams (mg) of caffeine — about 16 ounces of brewed coffee — 16 hours before bed may impact your sleep.

A 2013 study reported that downing 400 mg of caffeine 6 hours or less before bed had significant effects on sleep disturbance. Winter recommends cutting off caffeine consumption 4–6 hours before bedtime.

5. Screen time

Put down the smartphone! The blue light emitted from phones, tablets, laptops, and TV screens suppresses evening melatonin production and decreases sleepiness.

Winter recommends ceasing the use of any devices 2 hours before bed. You may also consider wearing blue-light blocking glasses at night.

6. Other sleep disorders

Delayed sleep phase syndrome isn’t the only disorder that can make you sleepy but not tired at night.

Sleep apnea and restless legs syndrome can do the same. In sleep apnea, breathing repeatedly stops or is very shallow, then starts again. With restless legs syndrome, your legs feel uncomfortable, triggering you to want to move them.

Both conditions can disrupt nighttime sleep, which then causes daytime sleepiness.

7. Diet

The connection between diet and sleep is a bit unclear.

In a 2019 study

, researchers looked at excessive daytime sleepiness and diet. They found that replacing 5 percent of one’s daily caloric intake from protein with equal amounts of saturated fats or carbs increased risk of daytime sleepiness.

On the other hand, replacing saturated fats with unsaturated fats, protein, or carbs reduced the risk of excessive daytime sleepiness.

They conclude that dietary changes may help people with sleep disorders.

A 2016 review found that high-fat diets were associated with less REM sleep, more deep sleep, and increased arousal from sleep. High-carb intakes were associated with more REM sleep, less deep sleep, and falling asleep faster.

However, the study’s authors say more research is necessary to determine if any one eating pattern promotes or impairs nighttime sleep and daytime energy.

Naturally, being tired during the day can sap productivity — and possibly make you irritable.

A regular, consistent sleep and wake schedule is Winter’s top suggestion for anyone who’s tired but can’t sleep.

You may also want to shift your bedtime, he says.

Think about it like this: You don’t sit in a restaurant for an hour just because it’s lunchtime — you go when you’re hungry. Why lie in bed and wait around for sleep? Hold off on getting between the sheets until you’re tired, and only do things that won’t stimulate your mind leading up to that time.

Then, follow the usual good sleep practices:

• Keep your bedroom dark and cool, between 60–67°F (15–19°C).
• Consider leaving your phone and other devices in another room.
• If noises disturb your slumber, try earplugs or a white noise machine.

Also stick to calming activities before bed, such as reading, journaling, or meditation.

If anxiety makes your brain hum at night, set aside 20 to 30 minutes of designated “worry time” during the day, ideally at least 2 hours before bedtime, suggests Michelle Drerup, PsyD, a psychologist with the Cleveland Clinic Sleep Disorders Center.

Journal on what’s worrying you. Then write down solutions to address those concerns.

At night, when you’re tempted to let your mind race, simply remind yourself that you’ve dealt with things and need to let it go. Or tell yourself that you’ll worry during your set time tomorrow — but now is the time to sleep.

If you try a few of these remedies and still wonder “Why am I tired, but can’t sleep?” talk to your doctor.

“Nobody comes into my office and says, ‘I kick my legs 400 times in the night,’” Winter says. “They say, ‘I can’t sleep.’” By telling your doctor about your sleep problems, they can ask questions and, if necessary, run some sleep tests to diagnose what the underlying problem is. Then you can receive the proper treatment to address the cause and help you sleep better.

Winter doesn’t recommend sleep medications unless someone has a condition such as restless legs syndrome, is a shift worker, or is trying to prevent jet lag before a trip.

“When we use a sedative like Ambien, Benadryl, or melatonin, we confuse sedation with sleep. That reinforces the belief that something is wrong with your sleep,” he says. “But it does nothing positive for sleep, it just induces sedation.”

If you’re still curious, since sleep medications can have side effects and impact certain health conditions, always try other remedies first and talk to your doctor or a sleep specialist before taking any sleeping pills. They can help you determine which may be best for you.

If you’re tired but can’t sleep, it may be a sign that your circadian rhythm is off.

However, being tired all day and awake at night can also be caused by poor napping habits, anxiety, depression, caffeine consumption, blue light from devices, sleep disorders, and even diet.

If you keep saying, “I’m so tired but can’t sleep!” and everyday sleep remedies don’t help, talk to your doctor. They can help determine the underlying problem and recommend solutions that will help you get restful sleep so you have daytime energy.

Brittany Risher is a writer, editor, and digital strategist specializing in health and lifestyle content. She’s written for publications including Elemental, Men’s Health, Women’s Health, and Yoga Journal.