Sleep is simply a natural periodic state of rest for the mind and body, in which the eyes usually close and consciousness is completely or partially suspended so that there is a decrease in bodily movement and responsiveness to external stimuli. This could be done at anytime of the day, but usually at night.
Inasmuch as there is need to put the mind and the body to rest, probably after the day’s work, as it is in most cases, a study has said that too many hours of sleep could lead to memory loss.