I would also suggest that you might be moving something that you aren't aware of. I would surmise that it would be your eyes, they are a dead giveaway to your body that you aren't asleep so it will delay putting you into total paralysis until those stop moving.

As robot_butler said, you could also not be timing your WILDs right. You can only successfully enter a WILD if you wake up to do it during or immediately before a REM cycle.