Same boat last year, and the single thing that broke the spiral for me was taking actual leave and completely unplugging, no Slack, no email, notifications off, the works. The first two days I felt guilty and twitchy, kept reaching for my phone convinced everything was on fire without me, but by day four my brain quietened enough that I could actually think again and feel like a person. Rest is not laziness and it's not a reward you earn, it's genuine repair your nervous system needs after months of running hot. Even if you can't take long, a few fully disconnected days help. Please also get it checked by a GP though, so you know whether it's burnout or something that needs more support.