Not being able to sleep usually means your brain is stuck in a state of heightened alertness that overrides your body’s natural drive to rest. This can happen for dozens of reasons, from stress and screen time to an underlying medical condition. Roughly 16% of adults worldwide, over 850 million people, experience insomnia, so if you’re staring at the ceiling wondering what’s wrong with you, the short answer is: you’re far from alone, and there’s almost always an identifiable cause.
Your Brain Is Too “On” to Sleep
The most common reason people can’t fall or stay asleep is something researchers call hyperarousal. Your body’s stress system, the same one that pumps out cortisol when you’re anxious or under pressure, doesn’t fully dial down at night the way it should. Studies on people with chronic insomnia show elevated cortisol and stress hormones across the entire 24-hour cycle, not just during waking hours. That means your nervous system is running a low-grade alarm even when you’re lying in a dark, quiet room.
This isn’t something you’re imagining. Brain imaging research confirms that insomnia involves a real disconnect between the systems that promote arousal and the systems that promote sleep. Chronic stress physically changes receptors in the brain’s emotional circuitry, particularly areas involved in anxiety and memory, making it harder for the “calm down” signal to win. The more nights you spend struggling, the more your brain learns to associate the bed with wakefulness, which deepens the cycle.
Three Patterns of Sleeplessness
Not all insomnia looks the same, and recognizing your pattern can help you and a provider figure out what’s driving it.
- Trouble falling asleep (sleep-onset insomnia): You lie awake for 30 minutes or more after lights out. This is strongly linked to anxiety, racing thoughts, and late-night screen use.
- Waking up repeatedly (sleep-maintenance insomnia): You fall asleep fine but wake at 2 or 3 a.m. and can’t get back down. Pain, breathing problems, and hormonal changes are common triggers.
- Waking too early: You’re up at 4 or 5 a.m. with no hope of returning to sleep. Depression and age-related circadian shifts often play a role here.
Many people experience more than one pattern at the same time. Clinically, insomnia becomes a diagnosable disorder when it happens at least three nights per week for at least three months.
Medical Conditions That Steal Sleep
Sometimes the inability to sleep is a symptom of something else entirely. A long list of medical conditions can disrupt sleep, including obstructive sleep apnea (where your airway partially collapses during sleep, causing repeated micro-awakenings you may not even remember), restless legs syndrome, asthma, acid reflux, chronic pain, arthritis, diabetes, thyroid disorders, heart disease, and nasal or sinus allergies. If you’ve been sleeping poorly for weeks and can’t point to an obvious life stressor, a medical cause is worth investigating.
Mental health conditions are just as important. Depression, anxiety disorders, PTSD, and ADHD all have well-documented links to insomnia. The relationship goes both directions: poor sleep worsens psychiatric symptoms, and psychiatric symptoms worsen sleep. Treating one without addressing the other rarely works well.
How Light and Eating Habits Shift Your Clock
Your internal clock is set primarily by light exposure. Specialized cells in your eyes are most sensitive to blue-wavelength light (the kind screens emit), and when that light hits your eyes after dark, it suppresses melatonin release and resets your molecular clock as if it were still daytime. Even moderate phone or laptop use in the hour before bed can delay sleep onset noticeably.
Late-night eating has a similar, if subtler, effect. Your digestive system sends timing signals to the same brain region that manages your circadian rhythm. Eating a large meal close to bedtime tells your body it’s still “active hours,” which can push your sleep window later. Night-shift workers are especially vulnerable to this double hit of mistimed light and mistimed food, but anyone scrolling and snacking at midnight is creating the same conflict.
Your Bedroom Setup Matters
Temperature is one of the simplest and most overlooked sleep factors. Your body needs to drop its core temperature slightly to initiate sleep, and a warm room works against that process. Sleep specialists recommend keeping your bedroom between 60 and 67°F (15 to 19°C). Anything above 70°F is generally too warm for quality sleep. For babies and toddlers, the ideal range is slightly higher, between 65 and 70°F.
Noise, light leaks, and an uncomfortable mattress compound the problem. None of these will single-handedly cause chronic insomnia, but in someone already prone to hyperarousal, a room that’s too bright or too warm can be the tipping point between a rough night and a decent one.
What Happens When You Keep Missing Sleep
A few bad nights are unpleasant but not dangerous. Chronic sleep loss, consistently getting fewer than six hours, carries real consequences. Your brain consolidates memories during sleep using a process that requires deep, uninterrupted rest. When that process is cut short, memory, attention, judgment, and decision-making all decline measurably.
Sleep is also when your brain’s waste-clearance system (sometimes called the glymphatic system) flushes out metabolic byproducts, including a protein fragment called beta-amyloid that accumulates in Alzheimer’s disease. Chronic sleep deprivation slows this cleanup, allowing toxins to build up over time. It also disrupts glucose metabolism and can contribute to insulin resistance. The emotional effects are just as concrete: sleep-deprived brains show weakened communication between the rational prefrontal cortex and the emotional amygdala, which is why everything feels more overwhelming after a terrible night.
The Most Effective Treatment Isn’t a Pill
Cognitive behavioral therapy for insomnia, known as CBT-I, is recommended as the first-line treatment over sleep medications. It works at least as well as prescription drugs in the short term, and its effects last longer. Most people who complete a course of CBT-I maintain their improvements after treatment ends, while people who stop taking sleep medication typically see their insomnia return.
CBT-I involves several components: restricting the time you spend in bed to match the time you actually sleep (which builds stronger sleep pressure), identifying and challenging the anxious thoughts that fuel nighttime wakefulness, and retraining your brain to associate the bed with sleep instead of frustration. It typically runs four to eight sessions and can be delivered in person, by video, or through structured apps.
Supplements: What the Evidence Shows
Melatonin is the most popular over-the-counter sleep supplement, but the evidence for it is mixed. It can help shorten the time it takes to fall asleep and may modestly increase total sleep time, particularly for people whose circadian rhythm is shifted (jet lag, delayed sleep phase, shift work). It’s not a strong sedative, and for garden-variety insomnia driven by stress or hyperarousal, it often disappoints.
Magnesium has somewhat stronger evidence, especially in older adults. Supplementation has been shown to improve sleep efficiency, reduce the time it takes to fall asleep, and decrease early morning awakening. One study found that a combination of magnesium, melatonin, and B vitamins taken one hour before bed for three months significantly reduced insomnia symptoms regardless of what was causing them. Typical supplement doses use around 175 mg of magnesium and 1 mg of melatonin, well below the megadoses some products market.
Neither supplement replaces addressing the root cause of your sleeplessness. If anxiety, a medical condition, or a misaligned circadian rhythm is the real driver, a supplement alone is unlikely to solve the problem.