I'm okay with water and such, but I get seriously terrified by limited visibility. You know the situations; the storm segment in L4D2's Hard Rain, some of the bunkers in Fallout, or almost the entirety of Bioshock. I will happily face down any monstrosity video games can throw at me, be it giant spiders, underwater levels or instakill chase sequences. But as soon as a game takes away my ability to see well, I nearly instantly rocket up to panic.
A side note: For those of you who have a particular schick for chase sequences, take a look at the PS2 game Haunting Ground. Survival Horror where almost the entirety of the threat comes from immortal stalkers that are hunting you, that you can never kill, and are never truly safe from. And the chase music... that damned chase music...