That's (sort of) the concept behind Narcosis, a survival game in which an industrial diver finds himself trapped at the bottom of the sea, desperately searching for oxygen and a way back to the surface before he loses his sanity completely.
It's actually not so much the local wildlife that makes up the horror here, but the alien nature of your surroundings anditself - the hallucinations disorientation, and confusion caused by breathing nitrogen and other gases under high pressure. Are you losing your mind or are you really in danger? That could make for some truly excellent horror. you can get a sense of that in the recently released in-game trailer, above.
And if you're brave enough, you can brave the ocean depths with an Oculus Rift. Narcosis is fully Rift-compatible, which should make the unsettling environments and bizarre creatures you'll run into about 90% more horrifying. Lovely.
Developers Honor Code have been working on Narcosis since 2013, when it began life as a school project, but they've only recently began to focus on it with the intention of a full retail release. They're hoping to have it ready by the third quarter of 2015, and you can find out a bit more on the.