Yep. Sounds like a night terror. Are they occurring around the same time each night? For my son, they were between 12 and 1 (that's a fun time to deal with a screaming child!). What I read (Solving your Child's Sleep Problems), is that its like when you wake up all disoriented in the middle of the night and it takes you about 2 seconds to figure out where you are . . .for a child, they are stuck in that "state" for a good 15 minutes or so . . .all disoriented.
What we found is that we woke him up BEFORE the event to sort of "reset" his sleep cycle. So, since it was happening between 12 and 1, we would wake him up around 11:30. Get him up, maybe a little sip of water and then back to bed. It was easier because my son was 3 and we got him up to go to the bathroom.
If it still happened, we would just sit there with him (not touching him, because it made him more upset as well) and just let him know that we were there and to let us know when he was ready for a hug. Most of the time, he would just calm down on his own (sometimes would take up to a 1/2 hour to calm him down). The more you stay calm, the better it is. Calm voices, calm touch.
It is a rough, rough time. it took us about 3 months to get out of it. Then it happened maybe once a month and I can't remember when it happened last. Its a phase. I am sure its harder when they are little (my youngest will be 2 this weekend), because you can't really discuss with them what has happened. My older son never remembered any of the screaming or thrashing from the night before.