Final answer:
Stage 2 sleep comes before REM sleep and is marked by sleep spindles and a slowing of heart rate and respiration, serving as a transition to deep sleep.
Step-by-step explanation:
The stage of sleep that typically comes before REM sleep is known as Stage 2 sleep. This stage serves as a bridge between light sleep and the very deep sleep of Stage 3. It is characterized by a deepening relaxation of the body and the appearance of sleep spindles and K-complexes, which are bursts of brain wave activity that are believed to be linked to learning and memory consolidation. During Stage 2, an individual's heart rate and respiration slow and the body prepares for deep sleep (Stage 3). Following Stage 2, the body may enter Stage 3 non-REM sleep, often referred to as deep or slow-wave sleep, marked by low frequency, high amplitude delta waves. After a cycle through the stages of non-REM sleep, the sleep sequence typically progresses to REM sleep.