(sorry for the terrible quality, it was the best I could find)
Reflections in general have always scared the bajeezus out of me; not to mention, you're rather vulnerable in bathrooms (naked, no alternate exits, unsuspecting, possibly in a compromising position)... I couldn't sleep (or be around mirrors) for days after watching this.
To sum up what you saw, and summarize a bit of the movie, there's a demon in the mirror (an alternate universe) that possesses reflections and makes people kill themselves. Even though most of the horror starts off in just mirrors, any reflective surface, water puddle, knife, doorknob, window, etc, will do.
Edit: Added summary
(This post was last modified: 01-11-2013, 03:29 AM by CarnivorousJelly.)