The most common answer to this would be "to rest ofcourse!" But why is there a concept of 'rest' in the first place?
When there can be man-made robots which can work 24x7, why can't we? Why do we need to rest every 16 hours for 8 hours atleast!? Thats a lot of time!
Surely our body is thousands of times better than machines and robots. Our body can even cure itself in case it is damaged. Same goes for the mental part also. There should not be a conecpt of mental exhaustion too.
Hence, one of the possible explanations to this can be that - sleeping was not meant for resting! It was meant for something else, that we have forgotten now. No wonder, sleeping is a weird phenomenon then. We become absolutely unaware of our surroundings. Time doesn't feel absolute. We might as well be dead mentally. And to make things even more interesting, we 'Dream!'.
Here's an interesting analogy:
When you go to bed and wake up, if you had no clock in your room, no watch at hand, you cannot tell how much time has past. It feels like a very short time has gone by when actually, many hours have gone by.
Infact, if u leave aside the time taken for you to fall asleep (the time during which u r conscious),
it would feel like no time has gone by.
There's another phenomenon which would feel exactly the same and it has been proven to exist - time dilation by theory of relativity. If go on a ride on a superbike travelling at say 99% speed of light, and come back home in 5 minutes according to ur wrist watch,... at home actually hours would have gone by! You would have no idea how it happened.
Thus to conclude, I believe the purpose of sleeping is not just for rest. Sleeping and Dreams are vital pieces of the puzzle of the Truth of the Universe. Don't underestimate them. Everytime you go to bed, clear your mind and hope for some Enlightenment!
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