I used to do this constantly, too. It was debilitating mentally going over conversations and chastising myself for all of my 'mistakes' because I somehow felt I had to be perfect.
Then I realized I was applying a huge double standard against myself. I thought about how I would react if someone had said the same thing to ME, and for the most part, I would not have reacted at all. It would not have been the huge mountain of a problem I was making it out to be.
Looking at it this way, has helped me a great deal!!!!