From my experience it's really painful, the pressure makes your head and eyeballs feel like they're going to explode. I pushed through regardless but must've "freed" myself while unconscious, I had the worst headache of my life and didn't feel quite right in my head since. I made several hanging attempts actually and don't remember them that well, but I remember the pain, and I think I must've been doing something wrong. I sure hope people who succeed don't have a time as terrible as I did
I forgot to add, I think it did feel peaceful at some point right before passing out. It's been a few years though and I only remember the pain