Pregnant women tend to get less deep sleep and experience more sleep disruptions than normal, which reduces their sleep efficiency. Elevated levels of the hormone progesterone, also, are known to cause increased daytime tiredness. The genitals of both sexes become flush with blood during REM sleep, causing increased sexual arousal. Men become erect during each of their REM sleep cycles. The genitals of both sexes become flush with blood during REM sleep, causing increased sexual arousal.
Men become erect during each of their REM sleep cycles.
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