Are anxiety attacks like mental breakdowns?

The term. "mental breakdown" has no meaning to a doc because that term is used by people to mean almost anything. Panic attacks can make you feel like you are "going crazy" but you aren't!
Panic is dangerous. Yes, some people have indeed killed themselves during a panic episode...Get professional help: meds and therapy. Adjunctive self help through yoga/meditation/mindfulness/holotropic breathwork/tai chi are also very helpful in the long run.