Think about the last time you were sleep deprived. You might have been up all night working on an assignment and then had to get up at the crack of dawn to get to work. Think about how mean and irritable you were that day. You got angry at everyone around you and you felt extremely agitated. Then you went and downed five coffees to wake you up and instead made yourself more depressed, anxious and uptight. That is what tiredness can do to you.