Is it normal that i can't even think about deep water?

You know that image where we see the tip of the iceberg, the water line and the huge piece of the iceberg underwater? I used to be able to see that picture, but since a while back I cannot even see it (nor anything like that, as a matter of fact). Actually I'm getting chills just thinking & writing about it. I even feel the need to move my legs up because I get the feeling something will pull them if they are hanging on the chair.

The same happened when I saw a documentary about Titanic, with underwater footage. I was on my couch but I instantly got this ridiculous feeling that I had something behind my back (it's the best way I can describe it) and just got really freaked out and had to change channels (and this doesn't happen with animated oceans, like in Finding Nemo LOL)

The same with satellite images (specially the ones where I can see the beach and the sand beneath the water), pictures of the bottom of the sea (only when I see that endless blue, if it's a picture of a starfish or a fish, it's ok), caves (like those huge caves with stalactites) or even those really deep pools at dolphin shows!

A normal pool doesn't mess with me, and I can easily swim there or at the ocean, if I see the bottom. This is really weird..