Yes you are, Groo. I have to say that your amoeba idea is very much liked, but not quite what I had in mind. I always thought that they were a humanoid shape of some kind, without being recognizable as some other humanoid shape. Now I'm being confusing.
But I think your biggest fear could be a boggart, because you don't know what it will turn into. But then, wouldn't the fear of the boggart itself over ride the greatest fear you had?
Man, this reminds me of the whole "Well, I saw myself conjur the patronus, so I know I could do it, but if I hadn't, I probably wouldn't have a soul right now".