It depends on the addiction. Opiate addiction comes along with flu like symptoms, insomnia, restless legs/arms AKA crazy legs, and an ever present anxiety that you really really want some that will make you do some weird shit just to get it. Other addictions are more subtle, some worse, but all of them I've experienced have the same feeling of stress/anxiety that can only be cured by the vice they are caused by. Many are all in your head, or, can be overcome by willpower, but definitely not opiates