What is caffeine withdraw and what does it do to your body?

It increases your heart rate, hence can increase your blood pressure. When a person sleeps, their heart rate slows down. Caffeine does the opposite of that.

Caffeine can cause heart palpitations, which are very bad for you.

Also, having 'super-coffees' before work can leave you halfway through your shift with chronically shaking hands... trust me, I've done that more than once... >.<