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Someone who sleeps during the day

What is an appropriate word for people who can’t sleep at night but sleep peacefully in the daytime?

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My first thought was "vampiric" - which means this question might be possibly related. :^) –  J.R. Oct 29 '12 at 2:42
    
@StoneyB Why not vote to close as dupe then? –  Mr. Shiny and New 安宇 Oct 29 '12 at 3:22
    
When it's pathological, it is called narcolepsy or dyssomnia. –  Cerberus Oct 29 '12 at 6:26
    
@Cerberus Narcolepsy, however, is not a circadian sleep disorder. –  StoneyB Oct 29 '12 at 11:37
    
@Mr.ShinyandNew安宇 I think it really wants to be merged, not closed. –  StoneyB Oct 29 '12 at 11:39
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marked as duplicate by MετάEd, Mr. Shiny and New 安宇, jwpat7, StoneyB, Kris Oct 29 '12 at 15:38

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1 Answer

up vote 7 down vote accepted

A difficulty or inability to sleep at night is known as insomnia, and one who suffers this condition is an insomniac. Sleeping during the day and remaining active at night is known as "nocturnality". Nocturnal only applies to creatures who only sleep during the day as their normal circadian sleep pattern, and therefore doesn't apply to humans (although it is sometimes used colloquially).

I think that what you're looking for is delayed sleep phase disorder.

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