Each stage of sleep has a characteristic EEG pattern, and sleep is divided into two broad types: NREM (stages 1-3) and REM.
NREM Stages 1 and 2 are light sleep. During stage 1, you may experience hypnagogic sensations, like feeling as though you're falling. In NREM stage 3, deep sleep, brainwaves become slower and larger, and the body does most of its repair work.
REM is called paradoxical sleep because the brain looks nearly awake while the muscles are essentially paralyzed; it's when most vivid dreaming occurs.
After deep sleep we move back up through lighter NREM sleep and then into REM; this cycle repeats all night, with deep sleep concentrated early and REM growing longer and more frequent toward morning.
After missing REM, the brain enters REM more quickly and spends more time there, a catch-up effect called REM rebound.
Key terms
NREM sleep
Non-rapid eye movement sleep; includes stages 1 through 3.
NREM stage 1
The first, light stage as you drift off; hypnagogic sensations can occur here.
hypnagogic sensation
An odd sensation while falling asleep, like suddenly feeling you're falling and jerking awake.
NREM stage 3 (deep sleep)
Deepest NREM stage, with slower, larger brainwaves; when the body does most of its repair work.
REM sleep
Rapid eye movement sleep, when the eyes dart under closed eyelids and most vivid dreaming occurs.
paradoxical sleep
Another name for REM: an active, wake-like brain in an essentially paralyzed body.
REM rebound
After REM deprivation, the brain enters REM faster and spends more time there to catch up.
Watch out
Deep sleep dominates early in the night; REM increases as morning approaches – not the other way around.
The paradox of REM: brain active like waking, body essentially paralyzed.