Stage one: This is when your body first starts to fall asleep and, because it's the lightest of the sleep stages, it won't take much to wake up.
Stage two: Once you reach the second stage of sleep, your heart rate and body temperature begin to decrease while your muscles start to relax. This is how your body prepares to enter a deep sleep.
Stage three: Your brain waves have slowed down and now you're in the deep sleep phase. Now your body is achieving the important restorative sleep that helps your mind and body get ready for the following morning. Stage three sleep takes place during the first half of the night, and this is when your body builds muscles and bone, repairs and regrows tissues and bolsters your immune system.
Stage four: Also known as REM Sleep, stage four is just as critical as stage three. REM stands for "rapid eye movement," and it's during this stage that your brain stores all of the information from the previous day. REM sleep, which starts about 90 minutes after you first fall asleep, also occurs in stages. The first stage lasts about 10 minutes and each consecutive stage increases in duration, with the final period lasting up to an hour. When REM takes place, your brain takes all of the information from during the day, everything from memories to emotions, and files it away in your long-term memory. Your brain becomes more active during this sleep stage, and both your heart rate and breathing increases.
A good night's sleep requires all four sleep cycle stages. If you're restless during the night, or if you wake up and drift off again, you may not be getting the quality sleep you need. Try unwinding before bedtime by reading a book or listening to music. Steer clear of alcohol and caffeine and stick to a regular bedtime schedule.