In my experience, typically, children with night terrors are not in control, but are still awake. They may be sitting up in bed, appear frightened, staring with eyes wide open. They may also be sweating, breathing heavily, and complaining of seeing peculiar things or objects that are not really there. This period of terror may last for up to several minutes and then the child will usually go back to sleep. What distinguishes night terrors from nightmares is that the child does not recall the dream or event leading to the night terror, and in many cases, does not recall anything that has happened at all.
Although the exact cause of night terrors, nightmares, and other sleep disturbances is not understood, they are thought to be a result of waking up during a certain stage of the normal sleep cycle. Night terrors occur during the NON-REM sleep period. Nightmares, on the other hand, occur during another stage or during REM sleep. Night terrors are generally infrequent and usually stop on their own without specific treatment.

It should be borne in mind that in rare cases where night terrors are frequent or associated with sleep walking, it is possible that specific medications may be required, but this is rare. In general, most children outgrow both nightmares and night terrors. Some people remember the following morning, but some don't. There is no explanation to why some have no recollection of the events.
Prevention and Possible Cures

As Night Terrors usually occur between 15 minutes and an hour after the child falls asleep, gently awaken your child just before you go to bed yourself.
Tuck them in and then say goodnight.
Often, this disturbance of the sleep pattern will prevent them from having an attack that night. Worth a try anyway!

Another approach is to note the approximate time that a child has regularly attacks, then gently awaken the child, 15 minutes before he or she usually has the attack, then tuck them back into bed.

If none of that helps and the attacks are violent, talk to your doctor about possible medication.

If you find that your child is experiencing a Night Terror, the best response is to hug and reassure them. Agree with everything they say or do. Don't shout and tell them they are only dreaming, as this only seems to upset them more and can have an adverse effect.