For me, the relevant question is: Can I get what I need to get out of therapy without talking about the past and delving into the topics that make me feel like crap?

In my case the answer is no, and the things that brought me to therapy are pretty crucial to my life. So I'm sticking with therapy and talking about those crappy topics because I think it's the only way to work through them, even though it can be really difficult.

It's important to not make yourself do more than you can healthily tolerate, though, and you are the expert in what makes sense for you right now. You should always be able to slow down or switch gears if you need to.