I get the same kind of problem. I WBTB, and if I stay up too long, I can't go back to sleep. In fact, if I stay up AT ALL, I pretty much kill my chances for a WILD. I end up counting into infinity with no success and have to fall asleep the normal way.

The closest I ever got was from trying to WILD without a WBTB, where I actually got to sleep paralysis. I never got that far again.