I've heard it said that a hangover is a mini-withdrawal. If during one episode you put mass quantities of alcohol in your system and then abruptly stop, your body is still craving that alcohol and you wake up with what we call a hangover. It usually gets better after several hours or a day.
True withdrawal is more for people who abuse alcohol on a daily basis for an extended period of time. The body has become dependent on the alcohol and after a period of time without it, will go into withdrawals and that can be dangerous.