my ds is 16mo and was a very bad sleeper for the first year (usually woke between 2 and 4 times a night, would sometimes go straight back to sleep, but other times stay awake for hours) but since he turned a year hes been better and better, and now seems to sleep through most nights. But lately (about 3 weeks or so) about 4 nights out of 7, he will go to bed at 8pm as usual, no problems, but then wakes an hour or 2 later, screaming hysterically. It takes a while to calm him down, he is still sleepy, most of the time he has his eyes closed during these 'episodes' then falls back to sleep in my arms. Usually sleeps through after them. What are they? He sounds like he is in dreadful pain or something, or that he is terrified. I'm worried :(