Are you on any medications?
The only times I had problems like this was as side-effects. My mom once gave me Ambien to help me sleep and I had audio and olfactory (smell) hallucinations on it. Luckily, Ambien makes you so chill it didn't scare me at the time.
But if you have a history of hypochondria, I suppose it could be that. Have you recently read up on other conditions that have symptoms similar to what you're now experiencing?