The soul experiences sleep, waking, tiredness, refreshment, etc., due to the ego that makes it identify with the body.  One may ask why changes in the body in which it resides do not taint the soul.  Shree Krishna explains it with the example of space.  It holds everything, but yet remains unaffected, because it is subtler than the gross objects it holds.  Similarly, the soul is a subtler energy.  It retains Its divinity even while It identifies with the material body.