If you don't have a therapist, it's worth looking for one. Honestly, everyone should have a good therapist, especially these days.

I had a similar experience and for me it was burnout compounded by years of ignoring mental health problems. I took a break for most of the pandemic, got a good therapist and psychiatrist and I'm so much more functional than I was at any other point in my adult life. But I really needed the time and space to focus on fixing myself, something that can be impossible when working long hours at a startup.