Trouble sleeping usually comes down to one of a few culprits: your brain won’t quiet down, something in your environment or routine is working against you, or an underlying condition is disrupting your sleep without you realizing it. About 16% of adults worldwide, roughly 850 million people, meet the criteria for insomnia, so if you’re staring at the ceiling tonight, you’re far from alone. The good news is that most causes of poor sleep are identifiable and fixable.
Your Brain’s Clock May Be Off
Sleep is controlled by an internal clock in your brain that responds primarily to light. When your eyes detect fading daylight, your brain begins producing melatonin, a hormone that signals it’s time to wind down. At the same time, cortisol, your main alertness hormone, is supposed to drop in the evening and rise again in the morning. When this rhythm gets disrupted, whether by irregular schedules, jet lag, or too much artificial light at night, the result is a body that doesn’t feel tired when you want it to.
People with chronically disrupted daily rhythms tend to have elevated evening cortisol levels, which keeps the brain in an alert state right when it should be powering down. This is why shift workers, frequent travelers, and people with wildly inconsistent bedtimes often struggle to fall asleep even when they’re exhausted.
Racing Thoughts and Stress
The most common reason people can’t fall asleep on any given night is cognitive hyperarousal: your mind won’t stop. Worry, rumination, perceived stress, and general emotional reactivity all correlate strongly with difficulty falling and staying asleep. The relationship is also bidirectional, which makes it especially frustrating. Stress activates your thoughts, which keeps you awake, and then lying awake in a dark, quiet room with nothing to do gives your mind an unstructured, socially isolated breeding ground for more ruminative thinking.
This cycle explains why insomnia so often gets worse over time if left unaddressed. One bad night creates anxiety about the next night, which then causes the next bad night. Your sleep system becomes reactive, meaning even minor stressors that wouldn’t normally bother you can now trigger a night of wakefulness.
What You Ate or Drank Today
Caffeine has a half-life of about five to six hours, meaning half the caffeine from your 3 p.m. coffee is still circulating in your system at 9 p.m. For slow metabolizers, it can linger even longer. If you’re sensitive to caffeine, anything consumed after noon can interfere with sleep onset.
Alcohol is trickier because it actually helps you fall asleep faster, which is why so many people use it as a nightcap. But it wrecks the quality of what comes after. Alcohol suppresses REM sleep (the phase tied to memory, learning, and emotional processing) during the first half of the night. As your body metabolizes the alcohol, the second half of the night becomes fragmented, with more frequent awakenings and lighter sleep. You end up sleeping for a full night on paper but waking up feeling unrested.
Your Bedroom May Be Working Against You
Light is the single most powerful signal your brain uses to set its sleep-wake cycle, and the type of light matters enormously. Short-wavelength blue light, the kind emitted by phone screens, laptops, and “cool white” LED bulbs, suppresses melatonin far more than warmer light. Cool white LEDs suppress melatonin production by roughly 12%, compared to just 1.5% for traditional incandescent bulbs and 3.6% for warm white LEDs. Tunable LED lamps set to a warm 2100K color temperature reduced melatonin suppression to just 0.1%.
The practical takeaway: if you’re scrolling your phone in bed under bright overhead LEDs, you’re essentially telling your brain it’s still daytime. Switching to warm-toned lighting in the hour before bed and keeping screens dim or off makes a measurable difference.
Temperature matters too. A room that’s too warm prevents your core body temperature from dropping, which is a necessary part of falling asleep. Most sleep research points to a bedroom temperature somewhere around 65 to 68°F (18 to 20°C) as the sweet spot for most people.
Medications That Steal Sleep
Several common medications can cause insomnia as a side effect, and people often don’t make the connection. Beta blockers, widely prescribed for high blood pressure, suppress your body’s natural melatonin production. Certain antidepressants, particularly some SSRIs, can be stimulating and make it hard to fall or stay asleep. Oral steroids like prednisone boost cortisol production and mimic what stress does to the body, directly disrupting the sleep cycle.
Decongestants containing pseudoephedrine raise your heart rate and blood pressure and can cause insomnia, which is worth knowing if you’re taking cold medicine. Diuretics (water pills) don’t affect sleep chemistry directly, but they can wake you up repeatedly to use the bathroom. Even nicotine replacement products like patches and gum can cause vivid nightmares that jolt you awake.
If your sleep problems started around the same time as a new medication, that connection is worth investigating with your prescriber.
Medical Conditions That Disrupt Sleep
Sometimes the problem isn’t behavioral or environmental. Two of the most common medical sleep disruptors are sleep apnea and restless legs syndrome.
Sleep apnea causes your airway to partially or fully collapse during sleep, leading to repeated brief awakenings you may not even remember. The classic signs are loud snoring, gasping or choking during sleep (often noticed by a partner), and waking up feeling exhausted despite a full night in bed. It’s especially common in people who are overweight, but it can affect anyone.
Restless legs syndrome creates uncomfortable sensations deep inside the legs, described as crawling, throbbing, pulling, or an electric feeling, along with an overwhelming urge to move. Symptoms typically start or worsen in the evening, particularly when you’ve been lying or sitting still. Many people with restless legs also experience involuntary leg twitching and kicking throughout the night, which fragments sleep even further.
Sleep Changes as You Age
If sleep felt easier in your twenties, that’s not just nostalgia. Deep sleep, the most physically restorative phase, decreases with age across the adult lifespan. Men experience a steeper decline, losing about 1.7% of deep sleep per decade, while women tend to maintain more stable levels. REM sleep also decreases at a rate of about 0.6% per decade from age 19 to 75. Meanwhile, lighter sleep stages increase proportionally, meaning older adults spend more time in sleep that’s easier to disrupt.
This doesn’t mean poor sleep is inevitable as you get older, but it does mean the margin for error shrinks. Habits and environmental factors that didn’t bother you at 25 might become real problems at 50.
When Sleeplessness Becomes Insomnia
Everyone has occasional bad nights. Clinically, insomnia is defined as difficulty falling or staying asleep at least three nights per week for at least three months. About 7.9% of adults worldwide, roughly 415 million people, meet the criteria for severe insomnia. If your sleep trouble has crossed that threshold, it’s moved beyond “just stress” and may benefit from structured treatment.
What Actually Helps
The most effective treatment for chronic insomnia isn’t medication. It’s cognitive behavioral therapy for insomnia (CBT-I), a structured approach that retrains your brain’s association between your bed and sleep. The core technique, called stimulus control, follows a specific set of rules: only lie down when you actually feel sleepy, don’t use the bed for anything other than sleep or sex, get out of bed if you can’t fall asleep within 15 to 20 minutes and return only when sleepy, repeat this pattern as many times as needed through the night, wake up at the same time every day regardless of how you slept, and avoid napping.
These rules feel counterintuitive, especially the part about getting out of bed. But the logic is sound. When you spend hours lying awake in bed, your brain starts associating the bed with wakefulness and frustration. Stimulus control breaks that association by ensuring the bed becomes a strong cue for sleep and nothing else. Most people see meaningful improvement within a few weeks.
For the immediate term, the simplest changes that tend to have the biggest impact are keeping a consistent wake time (even on weekends), cutting off caffeine by early afternoon, switching to warm-toned lighting in the evening, and cooling your bedroom down. None of these are dramatic, but sleep problems are rarely caused by one dramatic thing. They’re usually the result of several small factors stacking up.