Normal sleep is a movement through the 5 stages of sleep. Each stage is defined by the electrical patterns occurring in the brain. Doctors pinpoint these stages by monitoring the brain's activity, generally using an electroencephalogram or EEG. During normal sleep, you will pass through each stage in order, going from stages one through four and the final stage REM then back again to stage one. A complete sleep cycle (the progression through one full round of stages) will last about 90 to 110 minutes.
What's Happening During the 5 Stages of Sleep?
Stage One: In the first stage, you are lightly sleeping, drifting in and out of sleep and easily being awakened. The eyes move slowly and your muscles show signs of slowing in activity. Some people feel sudden muscle contractions during this stage. This may lead to a sense of falling afterwards.
Stage Two: In the second stage, all eye movement stops. The brain begins to relax, which is evident by brain waves slowing. There may be occasional bursts of rapid brain function during this stage, but generally, everything is slowing.
Stage Three: The next stage is evident by further slowing of brain waves. Your body itself rarely moves. The brain waves are very slow at this point, so slow they are referred to as delta waves. This slowing may be interspersed with small, but fast, waves. Stage three is also the start of deep sleep.
Stage Four: In the fourth stage of sleep, the brain produces almost only delta waves, the extremely slow brain waves. Stage four is also a part of the deep sleep stages. Here, it is very hard to wake someone from their sleep. There is no eye movement and no movement of muscles. In children, the fourth stage is also the most common stage for bedwetting, night terrors or even sleepwalking.
Stage Five: Things change considerably in REM, the fifth stage of sleep. This stage of sleep is characterized as the dream phase, but there is much more going on within the body at this time.
REM: Your Most Active Sleep Stage
REM is your dream stage, and often considered the most interesting. Here, your breathing increases but is irregular and shallow. The eyes move rapidly and the muscles of the limbs are often paralyzed for short periods of time.
One unique fact about REM is that your brain waves increase, almost to the same level as when you are awake. Your heart rate increases, as does your blood pressure. During REM sleep, men may have erections and everyone experiences a fluctuation in hot and cold, as the body has a difficult time regulating its temperature.
Dreams happen during REM sleep. If you wake up and remember your dreams, that's because you were awoken during an REM period. As your body moves through the 5 stages of sleep, you should have between three and five REM periods each night. That could mean up to five dream periods.
As your body grows and changes the amount of REM sleep a person gets changes. For example, babies will spend about 50 percent of their time in this stage of sleep. On the opposite side, adults spend 50 percent of their sleep periods in stage two and only 20 percent in REM. As you age further, the amount of REM periods you get lessens. Older people have less REM sleep than any others.
Facts About Sleep Stages
There are many myths and facts about the five stages. You should know about some of them:
- REM sleep wasn't discovered until 1953 when new mechanics were installed which allowed doctors to track brain activity. Prior to this, doctors believes all brain waves ceased while sleeping.
- A lack of REM sleep does not lead to insanity, something believed for centuries. There is no correlation between the two.
- Patients suffering from clinical depression may experience some relief if they go without REM sleep. Doctor's haven't found the correlation as to why this has happened.
- Doctors recently found reasons to believe there is a link to the amount of REM sleep you get and how easily you can learn or remember things.
- Your body's organs still work while sleeping, but they reduce their activities significantly, depending on the stage you are in.
These stages are still something doctors are learning about through research. Sleep studies allow them to fully study sleep disorders including the effects on the stages.