Is REM sleep (Rapid Eye Movement), the same as dream sleep?
Studies of human sleep have established five well-defined stages, according to electroencephalographic (EEG) recordings and polysomnography: * Non-REM sleep (NREM), accounts for 75-80% of total sleep time: o Stage 1, with near-disappearance of the alpha waves seen in awake states, and appearance for the first time of theta waves. The stage is sometimes referred to as somnolence, or “drowsy sleep”. It appears at sleep onset (as it is mostly a transition state into Stage 2), and can be associated with so-called hypnagogic hallucinations. In this period, the subject loses some muscle tone, and conscious awareness of the external environment: Stage 1 can be thought of as a gateway state between wake and sleep. o Stage 2, with “sleep spindles” (12–16 Hz) and “K-complexes”. The EMG lowers, and conscious awareness of the external environment all but disappears. This occupies 45-55% of total sleep. o Stage 3, with delta waves, also called delta rhythms (1–2 Hz), is considered part of slow-wave
