How much sleep you actually need each night varies somewhat for each of us depending on our age (younger people typically need more sleep than adults) and our genes (some people are naturally shorter sleepers than others). But typically the sleep target for adults is between seven and nine hours each night, according to guidelines from the National Sleep Foundation. (16)
According to Rafael Pelayo, MD, clinical professor of psychiatry and behavioral sciences and a sleep specialist at the Stanford Sleep Medicine Center in Redwood City, California, “Sleep is a natural, restorative, physiological process characterized by a perceptual disengagement [meaning you tune out from whatever’s going on around you], and must be rapidly reversible.”
Sleep experts at Harvard Medical School’s Division of Sleep Medicine use a similar definition for sleep. They say it can be characterized as: (1)
A period of being less active
A function of the body typically associated with a lying down posture and closed eyes
A process whereby you’re less responsive to external stimuli
A state of consciousness that’s easy to get out of (unlike other states of consciousness, such as hibernation or coma)
Being associated with certain brain wave activity patterns and certain physiological changes, including a drop in blood pressure and body temperature
Regardless of the words used to describe it, the bottom line is that we need sleep to function, Dr. Pelayo says. It’s a critical process that allows the body to function and stay healthy — and it’s especially important for the brain.
That recommendation, along with additional recommended sleep times for younger children, adolescents, and older adults, is based on the amount of sleep associated with the best health outcomes in a number of areas, including things like mood, learning, accidents, hypertension, heart disease, diabetes, and pain.
But Pelayo says don’t get too concerned about banking a specific number of hours of sleep each night. “The issue is waking up refreshed,” he says. “You should never wake up tired. If you do wake up feeling tired, something is wrong.”
Waking up sleepy could be an indicator that the quality of your sleep is poor. Maybe you’re spending too much time in light sleep, and not getting enough restorative deep sleep, for example, Pelayo says. If that’s the case, you should ask your doctor about getting checked for a sleep disorder, or see a sleep medicine specialist.