Autonomic System & Sleep
topic
Sleep involves systematic switching of the autonomic nervous system between parasympathetic dominance during NREM sleep (slowed heart rate, reduced blood pressure, diminished sympathetic tone, promoting cardiovascular recovery) and the unique REM state of autonomic lability (marked by variable heart rate, blood pressure surges, and sympathetic activation that explains the elevated risk of cardiac events during REM, particularly in REM rebound after deprivation).
Role
The cardiovascular recovery that occurs during NREM sleep — the nightly reduction in blood pressure known as 'nocturnal dipping' — is a physiological process whose absence is an independent predictor of cardiovascular disease risk, stroke, and all-cause mortality. Non-dippers (people whose blood pressure does not adequately reduce during sleep) have measurably higher cardiovascular risk even when daytime blood pressure is normal. Most people managing cardiovascular risk through diet, exercise, and medication are entirely unaware that sleep quality is an independent cardiovascular risk variable of comparable magnitude — because it is almost never discussed in standard clinical cardiovascular care.