Imagine someone wants to go to sleep at midnight and wake up at 7.30 am, so that they get an ideal five sleep cycles (7 1/2 hours).

First scenario: they go to bed at 11.30 and fall asleep within 15 mins, so they get 7 hours 45 minutes of sleep. Their alarm will probably wake them up at the beginning of a new sleep cycle.

Second scenario: they go to bed at 11.30 but can't sleep, and toss and turn for 45 mins, so they get about 7 hours and 15 minutes of sleep. Their alarm probably went off towards the end of their last sleep cycle.

The question is: which scenario could be more detrimental to one's health in the long term? Would it impact your sleep health more to wake up at the beginning of a new sleep cycle, or towards the end of the last one?

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  • There's a legitimate question here but you've posed it as so much about you that it's off topic. Can you delete all the stuff about you and ask the underlying question instead? – Carey Gregory Jan 14 '19 at 5:21
  • I can't find the site rules that say it's a problem to make a question personal, and in any case I was using myself as an example to illustrate the question. I've edited it in any case – Lou Jan 14 '19 at 9:13
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    Thank you for the edits. The prohibition is on personal medical advice. – Carey Gregory Jan 14 '19 at 12:50
  • Ah thank you, I appreciate the clarification :). – Lou Jan 14 '19 at 15:40

Generally, NREM phase 3 (N3) also known as deep sleep, is considered to be the sleep phase in which the body rests the most and people suddenly awakened during this phase may have unpleasant sensations and feel confused inmediately after waking up as noted by the National Sleep Foundation.

A typical sleep cycle may range between 70 to 100 minutes and N3 happens approximately about 30 minutes after the person falls asleep (after about 5 mins in phase N1 and 25 mins in phase N2). N3 itself only lasts for about 3 to 8% of the total time of all the sleep cycle. Another important note is that as the night progresses, the phases of sleep cycles shift a little bit in terms of the time they last: N3 progressively becomes shorter while N2 and REM phases become larger.

Given the latter, the answer to your question would be neither. The most detrimental case in the long term would be if the person keeps being woken up while in N3, that is about 30 mins into one of the first sleep cycles of the night and a bit more than that in the last cycles of the night due to N2 increasing. From the two scenarios you propose, you could argue that one would probably make a "smoother" transition between sleep and alert if the person is woken up while in N1 (start of the sleep cycle) since that is the phase in which it takes the least effort to wake up someone compared to all the other phases including REM.

Reference: Sleep physiology chapter in Sleep disorders and Sleep Deprivation: An Unmet Public Health Problem

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