Sleep 201

Mental arousal. Stress and worry can keep the mind active at night, making sleep difficult even when someone feels tired. Anxiety disorders can also affect sleep. This is one reason that feeling exhausted and being ready to fall asleep are not always the same experience. 2

A reinforcing relationship. Worry about not sleeping can make insomnia worse, while disrupted sleep can affect mood and concentration. Stress may contribute, but it does not explain every sleep problem. 17

Chronotype and timing. Some adults naturally feel sleepy and wake earlier; others tend later. This variation is called chronotype. A timing mismatch occurs when the intended sleep period conflicts with the internal clock. Night work and travel across time zones can create this mismatch: the local schedule changes before the body clock fully adjusts. 3

Seasonal changes. Daylight helps set the body clock, so changes in day length can influence sleep timing. Seasonal affective disorder is a distinct, recurring seasonal pattern of depression; winter-pattern SAD can include oversleeping, while summer-pattern SAD can include insomnia. Seasonal tiredness alone does not establish that diagnosis. 34

Caffeine and nicotine. Caffeine blocks adenosine signaling, masking part of the drive for sleep without replacing sleep itself. Nicotine is also a stimulant. Both can interfere with sleep. 35

Alcohol. Alcohol may initially make someone sleepy, yet sleep can become lighter and more interrupted during the night. Falling asleep more easily does not necessarily mean sleeping well. 6

Medicines. Some prescription and over-the-counter medicines can disturb sleep. Effects differ between medicines, and the condition being treated may also matter. Medication-related sleep changes require individual interpretation by a medical provider. 26

Aging. Sleep often becomes lighter and easier to interrupt with age, and sleep timing may shift earlier. This does not mean older adults no longer need adequate sleep. Changes in health, such as persistent pain or nighttime urination, can also break up sleep. 2

Hormones and health. Hormonal changes during pregnancy and menopause can affect sleep. During menopause, hot flashes and night sweats may cause awakenings. Physical symptoms, mental health and medicines can interact, so a change in sleep is not automatically explained by age or hormones alone. 12

Insomnia. A sleep disorder involving difficulty falling asleep, staying asleep or both despite adequate opportunity to sleep, with effects such as tiredness, poor concentration or mood changes during the day. It can occur on its own or alongside other conditions. 7

Sleep apnea. Breathing repeatedly slows or stops during sleep. Obstructive apnea involves upper-airway blockage; central apnea involves the brain’s signals to the breathing muscles. These are different mechanisms. 8

Restless legs syndrome. An urge to move the legs, often with unpleasant sensations, that is worse during rest and usually in the evening or at night. Movement temporarily relieves the symptoms. It is not simply restless sleep. 9

Other sleep disorders. Narcolepsy affects the brain’s control of sleep and wakefulness, causing excessive daytime sleepiness and often disrupted nighttime sleep. A person can have more than one sleep disorder; these short descriptions are not a diagnostic checklist. 910