Sleep

Sleep is a reversible, recurring state of reduced awareness and responsiveness during which the brain and body carry out restorative processes essential to health.

Sleep is not a single uniform state. Over a typical night the brain cycles several times through non-REM sleep, which deepens from light stages into slow-wave sleep, and REM sleep, the stage in which most vivid dreaming occurs. Two systems govern its timing: a circadian clock in the hypothalamus that tracks the roughly twenty-four-hour day, and a homeostatic drive that builds the longer a person stays awake. Adults generally need seven or more hours per night, while infants, children and adolescents need more, and dogs and cats sleep in many shorter bouts spread across the day.

Sleep is assessed by asking about bedtime, time to fall asleep, awakenings and daytime function, by sleep diaries and questionnaires, and, when needed, by polysomnography, an overnight recording of brain waves, eye movements, breathing and muscle activity. Common problems include insomnia, sleep apnea, circadian disruption from shift work or travel, and restless or fragmented sleep in aging pets. The endocannabinoid system participates in the regulation of sleep and wake cycles, and cannabinoids have been studied for sleep complaints, but the human evidence is early and inconsistent, and no cannabidiol product has an approved use for sleep.