The only way they would be able to tell is if you were completely honest with them about or moods and psychological background and any issues it presents. If it's type two bipolar, (the mild version) it may not impact your life enough to be a HUGE problem.

A doctor isn't going to always see if it you are completely honest about yourself and any problems you are having....if you tell them everything is fine they won't know anything. Many of are good at putting on masks over our problems and hiding them.

It's not something that is as obvious as a mark on your face...