I've been dealing with these for about a year now, my son is 2 1/2. The first time he had one I almost called 911, I thought he was in serious pain, it was so scary. I did a lot of reserach on them & found ways to help prevent them, my son doesn't have them as often, but still does from time to time.
Here are two websites that really helped me. I read the message board on the second website & found some helpful ideas.
http://pediatrics.about.com/cs/sleep/a/night_terrors.htm
http://www.nightterrors.org/
A few things that we tried that did reduce the frequency were:
*lavendar bubble bath & a consistant sleep schedule with wind down time before bed (including his bath).
*music at bedtime & I play it sometimes during the terrors, I just use a baby einstien music cd.
*make sure they are not overly hot while they sleep, some kids don't like the footed pj's but more importantly be sure they aren't too hot, it can trigger a NT.
during a night terror I just usually calmly ask him questions every once in awhile to see if he is awake or not, that is usually how I can tell when it is over, when he starts responding to me. "where is your nose?" "do you want some water?" stuff like that. I use to do that with a book & ask where the babies nose, eyes, etc, were when he was younger but now he is too out of control to get him to sit with me.
It's really a hard thing & a helpless frusterated feeling while your going through it.
Good luck!!
T.