This may sound strange but I have an irrational fear of the sea. I'm not a swimmer, in fact I despise the activity, but this has nothing to do with my fear. I've also been on boats, and have yet to get see sick; again not a cause.
This fear has a little to do with the unknown. I like to think, that as the sea is relatively unexplored, that there are things down there that we have yet to see. Take those evil neon fish for example. How mental are those things. All fangs and lights. Those and the fabled giant squid, which only ever seems to wash up in bits (Does this not imply there's something even bigger...?)
Anyway, my irrational fear mainly comes from video games. And of those, mainly Tomb Raider. Whenever there is an instance where you have to swim a great distance my fear is released. I think it comes down to the fact that you can be attacked from any direction. I remember being scared in the midst of a red sea level on Shadowman 2 I think, and then going to see Saw at the cinema. Back to the point. Tomb Raider is the main culprit though, and more specifically Tomb Raider 2. There's a whole section base at the bottom of the see, getting attacked by sharks and sneaky eel things that dart out at you from the black rocks. Cue pant change.
There havn't been many other instances over the years but I recently begun playing Tomb Raider Underworld on Xbox 360, and again, I had to change my pants. As you may or may not know, the first level takes place, once again, at the bottom of the sea. You've got scuba gear so air isn't a problem. But this time around, the Hi Def graphics don't help to ease my fear. All I'm saying is at one point I literally had to pause the game to catch my breath, and then there's this thing just watching you and you think "Will it get my if I swim past it? It is blind after all". I still don't know the answer to that question, too scared was I to try.
So I guess, to make a point with this post, Tomb Raider is still ace, video games can have an emotional effect on the players, and the sea is scary.