Sideways screen bug, was there an update???

[Despair]

Well me and a friend of mine hardly even find time to play and he doesn't have a great computer but when we do have time we play this game, he tried to play today though and his screen just kept tilting 90 degrees and doing all kinds of werid ♥♥♥♥♥ (I didn't actually see it) he said his screen was 'inverted' even though later on I showed him a video and it was the same thing he said, even though it was the 90 degree turn bug, anyway is there a way to fix this? I have a lot of mods some sourcemods as well and I host the servers locally, this has never happened before and I haven't added any mods recently, but we both got the 'Finalizing game instalation' today even though we clearly didn't re-install it or anything, not just that but I have some survivor mods and the fps arms were all broken and mutated, sometimes they flicked back to the original survivor arms (non modded ones which were also heavily mutated) and then flicked back to the modded (but clearly mutated) arms of the custom survivor mods. I'm wondering if any of this is related...

[Capt Marvelous]

I doubt it. I experienced it once or twice in the 5 years that I have this game. I shut the game and steam down and to be safe, rebooted my computer. I haven't had the problem since.