This doesn't surprise me.
The concept of A Nightmare on elm Street is perhaps the most disturbing thing I've ever heard about in my life. The idea that some unkillable spectre awaits you in your dreams is insane. Can you imagine how you feel when you haven't had enough sleep? Well, add the tension, nervousness, and paranoia that your mind and body would have to endure... that would be the most insane thing ever.
Sleeping, you've gotta feel like you're at a state of rest. Knowing that there's something lurking for you when you sleep could turn a person insane.