Boss bugged, exited game, profile gone

Playing offline.
I was in the middle of the boss battle with Yex (and as a side note, this battle is a royal pain in the ass because Yex goes invulnerable again so often and so quickly that I sometimes after beating his mob I couldn't even get a single shot in before he was invulnerable again).
Suddenly things started going weird. First all the heads up info (ie my health bar, Yex's health bar) vanished off the screen. Shortly after, my companion got injured so I tried to run over and revive him, but the revive prompt wouldn't come up. Then my camera locked. I could move in all directions with WASD, but my view wouldn't rotate with the mouse so I was stuck looking in the same direction. It wasn't a mouse problem because if I hit ESC to bring up the menu, my cursor moved around fine. At this point I was getting my ass kicked because I couldn't turn to see where attacks were coming from or fight back.

So I paused and exited the game, because I didn't want to have to take a death penalty under those circumstances).

When I next restarted the game, my character profile was just gone. The only option available was to make a new profile and start from scratch.