I'm a bit of a hypochondriac when it comes to physical things (e.g. the typical "ohmigod-I've-got-a-headache-it-must-be-a-brain-tumour" thing), but the worst thing is my fear of going insane...every week I'm worrying about a new mental illness, reading lists of symptoms and trying to convince myself I have all those things, then asking my family what they think, then getting stressed out when they tell me I DON'T fit those criteria! A while back it was schizophrenia, then it was bipolar, then it was Aspergers, then most recently it's been BPD...
I diagnosed myself with SA but that's different; my parents, a couple of doctors and the counsellor I see at uni actually agree with me, they're just not doing anything about it.