Pronanoia
The momentary heart-stop you get when you're looking at pornography and think there's a picture of you up there, and you mentally catalogue whether any ex's may have secretly taken a picture of you without you knowing it and then posted it on the internet.
I was browsing a porn blog when I was struck with an acute case of pronanoia! But I quickly realized I didn't have a twin sister, or a bathtub full of Jell-O.