Learn about the different stages of sleep, from light to deep sleep, after your head hits the pillow.
When you sleep, your body goes through several sleep cycles, each involving different sleep stages.
Most adults need seven to eight hours of sleep every night, and during this time, your body goes through different phases. The four sleep stages of sleep include:
- Three stages of N sleep, short for non-rapid eye movement (NREM) sleep. N sleep occupies about three-quarters of an adult’s sleeping time and is identified in stages: N1, N2, and N3 or deep sleep. NREM is the first phase of sleep your body slips into.
- The fourth stage of sleep is R sleep, or REM sleep. This stage of sleep is characterized by quick eye movements and facial and finger twitching. Most dreams happen during R sleep. Sleep patterns vary according to age. Most adults go through four to six cycles of all the stages of sleep — each cycle usually lasts between 90 and 110 minutes. Kids go through much shorter sleep cycles. For example, a 1-year-old may experience a sleep cycle that lasts only 45 minutes. By the time a child is about 10 years old, his sleep pattern will closely resemble that of an adult.
REM Sleep Confusion
While rapid eye movement (REM) sleep gets a lot of attention, researchers are still trying to decipher the biological purpose of REM sleep, according to Lisa Shives, MD, a sleep specialist at Northshore Sleep Medicine, in Evanston, Ill., and spokesperson for the American Academy of Sleep Medicine.
Dr. Shives says that a common misperception about sleep is that people mistakenly think REM sleep is deep sleep. “Deep sleep is stage 3. We also call it slow wave sleep, because that’s what the EEG [electroencephalogram] looks like.”
“The reason there’s confusion is because REM sleep is considered very important to feeling refreshed and having good cognitive function,” says Shives. “There’s a lot of talk about REM sleep, and people think deep sleep is the only good sleep.” Shives agrees that REM sleep is very important — one of its peculiarities is that it remains stable during a person’s entire lifetime, from the age of 6 to 96.
While REM sleep involves about 25 percent of sleep time throughout our lives, deep sleep rapidly declines even as we enter our 20s, says Shives. She says it’s very normal to see 50-, 60-, or 70-year-old men who don’t experience deep sleep. “We do know that sleep becomes more difficult and more fragmented as we get older, and people have more sleep complaints,” she says.
Confusion also abounds about deep sleep. “When we say ‘deep sleep,’ people think we mean something more,” says Shives. Deep sleep literally means the sleep that is hardest to wake up from. “We’re not sure it’s somehow qualitatively better for you physiologically.”
The Debate About REM Sleep
“Sleep doctors are obsessed with REM sleep,” continues Shives. “To a sleep doctor, there are three states of being, not just sleep and wake — it’s REM, non-REM, and wake.”
REM sleep is unique. “Everything in the body is different during REM — your hormones, your breathing, your heart, your immune system, your muscles, your cardiac,” explains Shives. “But we don’t know why. We don’t know the evolutionary purpose of it. We know that if you don’t sleep, you’ll go crazy and die, but we also know you don’t have to have REM.” The big question stumping current sleep doctors and researchers is how this unique physiological state is not necessary for life, but may be necessary for well-being.
By Clare Kittredge – Medically reviewed by Lindsey Marcellin, MD, MPH
DEC