It sounds more like an anxiety disorder to me. Hypochondria is more concerned with medical worries - people convinvce themselves that they're ill to get attention from the doctors. They may not even realise they're doing it.

I think I know what kind of thing you're talking about though. More like imagining situations which you really don't want to be thinking about because they're upsetting, or depressing?

Generalized Anxiety Disorder:
http://www.adaa.org/GettingHelp/Anxi...orders/GAD.asp

Hypochondria:
http://en.wikipedia.org/wiki/Hypochondria