Well, I can't tell you what it is, but I can tell you with almost certainty what it isn't and that would be cancer... I am saying that because the doctor found a discoloration on my retina in 2002 (also my dad's a few years ago) and he checked it periodically and was always happy that it was FLAT. So I would think anything sinister on your eyeball would be raised. And even that isn't sinister because I was thinking maybe you had (I can't spell this, so I'll sound it out!): Ping -you- lick- you - lie, that's raised but totally benign.
I totally understand the what if thinking. It just doesn't stop. Just recently I had 4 things at the same time (colon cancer, kidney failure, MS and a brain tumor) when I stop to think about it, that is insanity! But then my mind goes to, "Well of course I can't have all 4, but I MUST have ONE of them! But which one??" It's a never ending cycle.
You know what does help though. You think of what you are worried about (any symptoms, maybe your eye spot) and ask yourself, "Would a NORMAL person even notice this?" many times that is answered with a resounding, "No!"