Your heart rate and blood pressure are different during sleep, and they change depending on what phase of sleep you’re in. Heart rate and blood pressure go down and are steadier during non-REM sleep. During REM sleep, they rise and are more varied, similar to daytime patterns. Changes in blood flow during this sleep period can also cause sexual responses (erections in men and an engorged clitoris in women). As daybreak approaches, both heart rate and blood pressure inch back up.