Both anorexia and alcohol can damage the body. Each can lead to organ problems and potentially organ failure, which may end in death in some cases. Both are dangerous diseases (anorexia and alcoholism) that can be treated, too.
Yes the alcohol causes the body to become de-hydrated so it is very important to remain hydrated and drink plenty of water ideally before, during and after consumption of alcohol.
your body reacts to alcohol as an allergic reaction, everyone is allergic to alcohol that's what gives us the buzz, it deprives the body of water, it would feel the same as getting lost in the desert...