Bad Sleeping Habits beginning at 13 months, HELP!!?

My son who is 13 months now has always been a pretty good sleeper. If he woke up I would tend to him (give him milk or a pacifier) and then he would go right back to sleep. Well the past couple of nights I have put him to bed and he has woken up about 2 hrs into it screaming and I cant console him!! He never does this!! So, I sit on the floor with him with the lights on dim and he walks over to the tv and starts banging on it because he wants to watch ELMO!! What the heck is going on and how do I stop this behavior before it gets out of hand. I will admit that I caved in....as soon as I turned Elmo on he cheered right up and went back to bed for the rest of the night once it was over. I am not the kind of person that wants my child to have a tv babysitter. Do you have any other suggestions for calming him down? I have never seen him this upset until this past week or so.