A good sleep will refresh you. During sleep you can pass through 4 phases: 1, 2, 3, and REM (Rapid Eye Movement). These stages can pass regularly from stage 1 through to REM, and begin at stage 1 again. This complete cycle lasts roughly 90 to 110 minutes.
In this stage, you drift in and out of sleep and are easily awakened. You are not deeply asleep although your eyes are closed. During stage 1, all your muscles are relaxing at one time and it is usually followed by sudden muscle contractions. Stage 1 is where that “falling” sensation occurs.
During this stage, eyes move slowly, brain waves become slower, heart rate slows and your body temperature drops. You’re starting to physically become more “at rest.
This is the deep, restorative sleep you want. This is when slow brain waves begin called delta waves. It is very difficult to wake someone from this stage. You are likely to feel disoriented when you are awakened. There is no eye movement or muscle activity. Your body is repairing and re-growing tissues, building bone and muscle. This stage helps to strengthen your immune system. During this stage, children are more likely to wet the bed, walk in their sleep or have sleep terrors.
This is the time when dreams are most likely to occur. In this stage, your brain weaves are increased to levels usually seen when you are awake. During this time heart rate increases and blood pressure rises. But, you may lose some ability to regulate temperature. Males develop erections in this stage. The first REM period is usually about 10 minutes, and it increases as you experience more sleep cycles. The last REM cycle is usually about 1 hour. Adults spend up to 50% of their sleep in stage 2 and about 20% in REM sleep; babies spend up to 50% of their sleep in REM sleep. You have less REM sleep as you age.