Which stage of sleep is characterized by irregular heart rate and respiration?

REM (Rapid Eye Movement) sleep is the stage of sleep that is characterized by irregular heart rate and respiration. During REM sleep, the brain becomes highly active, and this is when most dreaming occurs. The body's muscles are generally paralyzed, which prevents individuals from acting out their dreams. This stage also leads to distinct physiological changes, including variability in heart rate and breathing patterns, which can become erratic compared to the more stable patterns observed in other sleep stages.

Other stages of sleep, such as deep sleep and non-REM stages like Stage 1 and Stage 2, typically feature slower, more regular heart rates and respiration. During deep sleep, in particular, the body experiences the lowest levels of heart rate and breathing, facilitating recovery and restoration processes. Therefore, the variability seen in heart rate and respiration is a hallmark feature of REM sleep, distinguishing it from the more stable patterns seen in other sleep stages.