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What happens during a long sleep that makes people look odd when they have just woken up? Why doesn't the same phenomenon occur in the case of a person who lies down for an extended period of time, but stays awake? I've noticed that some nights seem to make a bigger difference than others in the appearance of the sleeper, but haven't noticed a pattern.

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Can you elaborate on what the characteristics of "looking odd" are? I think everyone has some sense of (or experience with!) what you're talking about, but in order to address things scientifically the specific characteristics (e.g., dark circles under the eyes) would be helpful. – jonsca Feb 13 '12 at 1:41
Not dark circles (that sounds more like long term lack of sleep); I'm referring to the sort of "puffiness" around the eyes and mouth. It's hard to describe without a picture. – Daniel Feb 13 '12 at 1:58
up vote 4 down vote accepted

Puffy eyes are caused by fluid build up in tear ducts from extended periods of lying down. Gravity from sitting or standing slowly drains them during the day. The crusty 'sleep' that accumulates in the corner of your eyes is the residue from basal tear liquid that has seeped out of the eye and evaporated during the night.

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