Well, I think Slender Sickness may have left me for a while, well everything except for ringing in my ears.
I've had this though: I wasn't really sleeping for three days, not counting the naps I had that may have been about 3 hours, and I wasn't eating normal food for two weeks, only cookies and juice. (All of this does not seem to have any effect on me)
These things happened to my best friend, too.
Also, when I was trying to sleep, just before falling asleep I always felt that someone was behind me, and it felt like something wrapped around my ankle or wrist, and when I talk with my best friend through Skype, she says she always ses a tall, black man behind me, or I see Slender Man behind her. So, that gives us one hell of a creepy experience, but we don't really feel so creeped out by this.