agonize (oneself) over
To worry excessively, especially about a decision or past action. Please stop agonizing yourself over this decision. It won't really matter which one you choose. There's no need to agonize over what you said to him. He probably doesn't even remember.
agonize (oneself) over someone or something
to fret or anguish about someone or something. Now, now, don't agonize yourself over the situation. Time cures all.