The past does not cause stress but who really knows what happened in the past. If you have ever read a newspaper article about something about which you had first hand knowledge, you know that is it rarely accurate or at least how you remembered it. And that is something that just happened. Things that happened 50 or 200 years ago are in the past, of course, but the truth is we have very little to go on with respect to what did happen.
A good demonstration of now "flexible" the past is law faculties. In twenty five years of being on the same faculty, I have seen one past come and replace another only to be reinterpreted to become a third past. People who fought tooth and nail to avoid hiring someone now take credit for the hire. People who favor a procedure because it gets them what they want claim it is "the procedure" when, in fact, there was no procedure. Over and over there is a new past so that it appears to support current largely self-interested goals.