I managed for years also. Sorta. I just didn't know I had anything wrong with me is more like it. And for years I worked at jobs that kept me physically busy so I don't think I would have noticed the mania anyway. But there were other signs that emotionally I was not balanced.
I have spent a good deal of my life fighting depression too. Took anti-depressants here and there but quit taking when I felt better. They probably just made me manic and again, I didn't know better.
Now though it has gotten worse and I am not happy with the me that is being projected to family and friends. And I am not happy with living with the roller coaster of emotions. So I chose to get help and make a change. It was hard because I really am afraid of medications.
But I can see where you could be Bipolar and feel like you can manage it. I don't feel it is impossible.
Good luck and I hope it works for you.