Thanks for the responses, folks - I know that a thought like this, even if it randomly occurred to me, wouldn't carry any weight at all if I weren't already feeling very anxious. I've always held the belief that if I were truly having a delusion, I wouldn't recognize it as being a ridiculous thought, but I read an article recently where a girl had mentioned that she had bipolar with schizoaffective tendencies (I think that's the correct term, not 100% positive) and that she had a delusion that her boyfriend had been replaced by an alien doppelganger. She said that at the time, she realized it was a crazy thought, which I always thought was impossible. I think deep down, my rational mind is still there, but it gets drowned out by the intrusive, anxious thoughts.
I think my #1 biggest fear with my anxiety/OCD is that I'm "crazy" or that I'm going to become schizophrenic or suffer from psychosis. It seems like I'm closer to that line, or more vulnerable, because I've already got one mental/emotional disorder, so I'm more likely to have another, right? It's comforting to know that many people with OCD and anxiety suffer from this same fear.