First off, the choices being only "Is this a past life?" or "Am I insane?" is preposterous. It is entirely possible that it is NOT a past life and that you are NOT insane. However, it is true that simply seeing things from his life and having headaches is not much information on which to assume that you were him. One of the most important things to remember about past lives is that our memories are flawed. Even from this life we remember only a very small portion of what we THINK we remember.
I don't think it's impossible that you were Adolf Hitler. Here's some questions to ask yourself. Do you remember anything that is not common knowledge? One of my past lives was a historical figure (I am not saying who publicly), and the memories I had did not come out in research about that figure until I had done some in depth research. Do you find yourself knowing words in German that you have never learned in this life? How do you feel when you do research on the Nazis? Remember, Adolf Hitler really truly believed he was doing what was best for his people (most of his friends still say that to this day), and if you feel angry about how people villify him, you might have either been him or been someone close to him. If you feel the way most people do about Nazis (hate them and what they did), chances are good that you are not in fact the reincarnation of Adolf Hitler. Lastly, do you look anything like Adolf Hitler? While it is true that not everyone looks similar in all their past lives, I have discovered that there is usually some kind of resemblance. It's usually in the eyes, but it can be cheekbones, stature or something else. I believe this might be because the soul shapes the body when the body is growing, but I'm not actually sure of the reason for this.
If none of this is true, it is unlikely that you are Adolf Hitler. Lots of people get headaches and most of them are not Adolf Hitler. Still I think it's a little extreme to assume you're insane just because you have these memories and headaches. The mind can invent memories, perfectly sane people do that all the time. Look into it if you don't believe me. I hope this helps.