SNL did a parody of that sort of thing: http://www.hulu.com/watch/11203/saturday-night-live-snl-digital-short-the-mirror#s-p11-sr-i2
I did not know that.
Pi.
Actually, the show House had one too: “Autopsy,” the second season episode with the little girl cancer patient, started with her having reality bending hallucinations in the bathroom.
It makes sense that the bathroom would be a good setting to add tension in this way. You’re exposed and vulnerable more so than other rooms of the house. Plus you have the trope of the medicine cabinet door being opened and then closed, only to show more than what was there before.