Why is sleep so important? Sleep is a critical aspect of our overall wellbeing both physically & mentally. There are two major phases of brain activity during sleep that we cycle through every night. These are called Non-Rapid Eye Movement (NREM) & Rapid Eye Movement (REM). During NREM sleep, the brain slows down which results in decreased eye movement & muscle activity. This is when the brain is preparing the mind & body to enter into a state of deep sleep. About 1-2 hours after NREM, we enter into REM sleep. This is when activity in the brain increases at a rapid speed & usually results in vivid dreaming! Throughout the night we go in & out of these two phases of sleep.