J. -
I don't have any advice - I just wanted to encourage you and say HANG IN THERE! My son, who is 20 months old, does the same thing. He sleeps about 12 hrs/night, 2 hrs nap in the daytime, and sometimes wakes from his nap crying and angry. I've tried rocking with him, having a snack ready when he wakes up, playing with him...Recently, I've tried treating it like a tantrum. I let him lay in the middle of the floor where I can see him while I fold laundry or watch TV or whatever. I've noticed that he looks at me for some type of response and if he doesn't get it then he kind of turns over and screams more until an interesting toy catches his eye, then he just goes and plays and boom, fit over. I also stopped running into his room when he wakes up screaming his head off because I think he expects me to come running in. Of course by now, I can tell the difference between his tantrum-type cries and his genuine help-me cries.
Rarely, he wakes in the middle of the night, crying and acting kind of hysterical, but when we go to check on him, his eyes are closed like he's still sleeping. We believe it's his version of night terrors or something like that, so we just comfort him and he generally wakes up a few minutes later looking confused and sleepy. Then we can lay him back down once he calms down and he goes right back to sleep.
Hang in there, honey! I don't think there's anything wrong.