What are sleep disorders?

Sleep can be divided into two types: rapid eye movement (REM) sleep and non-REM (NREM) sleep. NREM sleep has four stages of increasingly deep sleep. Stage 1 sleep is the lightest, while stage 4 is the deepest.

During normal sleep, you move cyclically through these types and stages of sleep. But if your sleep is repeatedly interrupted and you are unable to progress normally through REM and NREM sleep, you may feel tired, fatigued, and have trouble concentrating and paying attention while awake. Sleepy individuals are more likely to have accidents while driving, as well as other types of accidents.