The brain is in a constant state of tension between cells and chemicals that try to put you to sleep and cells and chemicals that try to keep you awake.
The neurons of your brain show vigorous rhytmical activity when your're asleep--perhaps replaying what you learned that day.
People vary in how much sleep they need and when they prefer to get it, but the biological drive for an afternoon nap is universdal.
Loss of sleep hurts atttention, executive function, working memory, mood, quantitative skills, logical reasoning, and even motor dexterity.
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