The sleep cycle of a human changes as we age. A newborn child has sleep cycles lasting only 45 minutes. By age 10, a child has sleep cycles between 90 and 110 minutes. This length of sleep cycle remains fairly consistent throughout adulthood. A sleep cycle is a series of sleeping states that ranges from light sleep to dreaming to deep sleep and back again. The completion of several sleep cycles every night is very important to good health.
Drowsiness
This is typically referred to as stage one sleep. Your eyes start to close, you lose track of time, and you flash in and out of consciousness. Even though this is considered the first stage of sleep, it is very easy to awaken someone in this condition. It usually lasts between 5 and 10 minutes.
Light Sleep
This is often referred to as stage two sleep. During this time your muscles twitch and relax unpredictably. Heartbeats slow down and the temperature of the body falls. It becomes harder to wake someone in this condition, but there are often physical reactions to noise and light. This stage lasts between 5 and 15 minutes.
Deep Sleep
Deep sleep covers both stages three and four. They are similar but stage 4 is deeper than stage 3. Brain activity drops to a very low level. It is difficult to wake someone in deep sleep. If they are awakened, they are often disoriented. Blood leave the brain and diverts to the muscles facilitating repair. This stage lasts between 5 and 15 minutes.
Progression/Regression
The normal progression during a sleep cycle is from stage 1 to 2 to 3 to 4, then back to stage 3 and stage 2. The brain falls into a deep sleep then comes out of deep sleep before finally dreaming. This entire process usually takes about 90 minutes.
REM Sleep
REM stands for rapid eye movement. This is where the eyes move back and forth beneath your eyelids as you sleep. This is also when you dream. REM sleep is believed to be very important to the health of the brain. When people are deprived of REM sleep they experience mental anguish. REM sleep is actually very similar to stage one sleep. Muscles twitch, heartbeats increase, and breathing becomes rapid. After about 15 minutes, the entire sleep cycle repeats itself.
