Formication

I appear to have contracted a (very mild) case of what I have learned is technically called delusional parasitosis-- the irrational belief that there are bugs crawling on one's skin.  Our household has recently been fighting an minor infestation of extremely small ants (possibly odorous house ants), which seem completely uninterested in all of the ant traps we've strewn around.  And once you've discovered ants crawling on your head a couple of times in a row, I think it's only reasonable that you might develop a bit of a twitch.