Everybody goes through five stages of sleep known as sleep cycles. During a sound night’s sleep, we progress from Stage 1 to Stage 4 and then to REM sleep in about 90 minutes. A good sleeper will move through four to six of these ninety-minute sleep cycles during the night, spending about 5% of the night in Stage 1 (light sleep), 50% in Stage 2 (light sleep), 20% in most profound phases of deep sleep which are Stage 3 and 4 and 25% in REM sleep. Deep-sleep periods are lengthier during early part of sleep, but as the night proceeds deep-sleep periods grow shorter and the duration of REM periods increases sometimes to the point where it may persist for an hour. We therefore optain most of deep sleep more during the first half of the night and the majority of our dream and light sleep in the second half. REM is not deep sleep. REM is also called dream sleep because it is when we dream. While dreaming, our brain and physical activity becomes more active, our heart rates increase, breathing speeds up, blood pressure increases. We are more apt to awaken from this stage and are more likely to feel alert when we do. But if we are awaken during the deep sleep of Stage 3 and 4, we will often feel groggy, confused or disoriented. It is normal to wake up six or more times during the night especially when we shift from one sleep stage to another. We normally fall back to sleep within seconds after these awakenings and don’t recall them in the morning.