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When we eat, finally we feel full. I know which mechanism causes the sensation of being full. But when we sleep excessively we often still want more sleep. Why does this happen? Is there a mechanism underlying this?

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Is this a universal phenomenon? – kmm♦ Jan 16 at 13:56
What you think dear Kevin? you didn't experienced? – MySky Jan 16 at 14:30
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i doubt there is a good answer to this one. I recently read an interview with the retiring head of the UCSF sleep center and he said 'to the best of our knowledge, the reason we need to sleep is because we get sleepy.' Not sure if there is a strong answer to a question like this ;) – shigeta Jan 16 at 16:13
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No answers, but some speculations: Perhaps "excessive sleep" simply usually happens when people are excessively tired? Or perhaps people who once in a while sleep excessively do it to "make up for lost sleep", but that it is not really possible to make up for lost sleep, and lost sleep in general might lead to lower quality of sleep. Low quality of sleep may make you want to sleep more. In normal cases where you get up early there is perhaps some sense of acuteness or danger that makes you relatively alert (at a cost, perhaps). – 5th Jan 22 at 1:40
People sleep in ~90minute long sleep cycles. Technically, if you decide to "sleep in" by 30-50 minutes, you may start the next sleep cycle and feel worse awakening from that. The logic behind this is that you wake up from deeper sleep. I don't know if there is hard science to back this up though – Alex Stone Jan 23 at 4:13

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Studies have proven somewhat the opposite of what you're asking

For example a study from 2004 - "The impact of extended sleep on daytime alertness, vigilance, and mood" found that,

Average daily POMS vigor and fatigue scores also improved during the sleep extension period

And thus concluded

Extended sleep leads to substantial improvements in daytime alertness, reaction time, and mood.

Whilst an older study from '73 -"Performance and Mood Following Variations in the Length and Timing of Sleep" found that,

Neither sleep duration, nor any other sleep parameter consistently correlated with the performance or mood measures.

The study does go on to state however,

Therefore, it seems reasonable to assume that the detrimental effects of acute changes in the length and/or timing of sleep were not directly related to any specific changes in the length or electrophysiological patterns of sleep, but to as yet unknown physiological changes resulting from the disruption of an established circadian rhythm of the sleep and wakefulness.

This perhaps suggests that the question which should be asked should not be why does oversleeping makes us feel tired, but why does the disruption of normal sleeping patterns make us feel tired?

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