I once read that depression and anxiety are like time travel.
When you are depressed, you are living in the past, dwelling on things that already happened. And when you are anxious, you are living in the future, worrying about things that *might* happen. And in either of those states, you are failing to live in the present.
I don't think I need to tell you that all that mental time travel isn't good for you. (And not because you'll put some kind of rift in the space-time continuum if you meet your former self or whatever.) But because you are ignoring the here and now in favor of the past or the future.
So, I'll say this (and this is what I say to myself when I catch myself in either of these states): The past already happened. You can't change it. You can't make it different. The future is going to take care of itself. Worrying about it isn't going to change it or make it different, either.