When You Sleep?
Stages of Sleep
stage 1, which is light sleep, we drift in and out of sleep
and can be awakened easily. Our eyes move very slowly and
muscle activity slows. People awakened from stage 1 sleep
often remember fragmented visual images.
Many also experience sudden muscle contractions called
hypnic myoclonia, often preceded by a sensation of
starting to fall. These sudden movements are similar to the
"jump" we make when startled.
When we enter stage 2 sleep, our eye movements stop
and our brain waves (fluctuations of electrical activity
that can be measured by electrodes) become slower, with
occasional bursts of rapid waves called sleep spindles.
In stage 3, extremely slow brain waves called
delta waves begin to appear, interspersed with smaller,
By stage 4, the brain produces delta waves almost
exclusively. It is very difficult to wake someone during
stages 3 and 4, which together are called deep sleep.
There is no eye movement or muscle activity. People awakened
during deep sleep do not adjust immediately and often feel
groggy and disoriented for several minutes after they wake
up. Some children experience bedwetting, night terrors, or
sleepwalking during deep sleep.
When we switch into REM sleep, our breathing becomes
more rapid, irregular, and shallow, our eyes jerk rapidly in
various directions, and our limb muscles become temporarily
paralyzed. Our heart rate increases, our blood pressure
rises, and males develop penile erections. When people
awaken during REM sleep, they often describe bizarre and
illogical tales – dreams.
More about REM Sleep
What Happens When You Sleep?
The Different Stages of Sleep
Source: National Institute of Neurological Disorders and