I had a similar conversation with a manager a few years back, and it went much better than I expected. It's tough, because on one hand you're literally saying to the boss, "I'm currently unhappy and unable to work at the level I expect of myself.", but hopefully they are able to empathize enough to want to work through it. It could easily go the other way, though. My advice is to be prepared for it to be a conversation that leads to you not working there anymore, but at the same time be open to being pleasantly proved wrong.
Also, burnout feels terrible. Really sorry to hear that. Good luck!
Also, burnout feels terrible. Really sorry to hear that. Good luck!