Okay, okay, nobody laugh at me....
I'm pretty much afraid of heights - not so much scared if I'm in something like an airplane or an amusement park ride, but if I'm not strapped to something, it scares the crap out of me. So ladders, Empire State Bldg balcony ledge, fire towers, etc. freaks me the heck out. And I know it seems silly that this fear should translate to swimming, but for some reason it does.
I went snorkeling in the Florida Keys after high school graduation and it freaked me out - amazed me at the same time, but freaked me out. My depth perception pretty much sucks most of the time, but really sucks in the water. Something about looking straight down through the water and thinking you're pretty close to the bottom and then seeing a big fish swim between you and the bottom and getting that dose of perspective freaks me out. I can only imagine what that would mean in really deep water where I couldn't see the bottom. I'm pretty sure I would have a major panic attack and become fish bait.
Also, salt water makes me nauseous. As in I'm a total wuss if I get water in my mouth at the beach while I'm swimming or if I'm siphoning water out of the tank. It makes me gag and I feel like I'm going to die. Hence being under water and having that happen could be problematic I would think.
I'm a little bit of a freak and I'm super weird - I know... I guess I just look at it and think that if I were meant to be a water beast, I would have been born with fins. Clearly I am a land mammal and that is where I shall stay.