NotEinstein
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A number of medical studies have shown that, overall, one's heart rate should slow down during sleep. But does this occur immediately after falling asleep? Good question.
The answer is no, not exactly. The heart rate might slow down a bit right after falling asleep, but it's not until you've been asleep for about 15-20 minutes that your heart rate really begins to slow.
Medical researchers have identified five stages of sleep. The first stage of sleep, Stage 1, occurs after falling asleep. This is a light sleep and may last for about 10 minutes. If you wake someone up during Stage 1 sleep, they might feel like they haven't slept. Stage 2 sleep gets a bit deeper and heart rate begins to slow; this might go on for 20 minutes. Stage 3 and Stage 4 sleep are deeper sleep, and brain activity changes and slows. Stage 3 and 4 are when the heart rate is the lowest.
The fifth stage of sleep, known as REM (rapid eye movement) sleep, may show increases in heart rate or changes in brain activity. REM sleep is when most people dream.
So, although a sleeping heart rate is overall lower than a waking heart rate, there is actually more variation in heart rate during sleep. This was confirmed in a study published in the journal of the American Heart Association: heart rate variability is higher during sleep than during daytime. While transitioning between different stages of sleep, your heart rate may increase or decrease with more variation than during your waking hours.
(http://circ.ahajournals.org/cgi/content/short/91/7/1918)
 Posted 5053 day ago
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