Night terrors are a sleep disturbance in which your child is not fully awake, but it screaming, crying or moaning as a result of a dream. They differ from nightmares in that they do not happen in REM sleep, and your child will have no recollection of it the next morning. These will affect you far more than they will your child.
What should you do?
Don't try to wake the child, and expect your attempts to comfort to be rebuffed - he or she isn't awake and does not know you are there. Unless it is necessary for your child's safety, do not try to restrain or control them.
Take the same precautions you would for a sleepwalker; keep the floor clear of trip hazards, fasten a stair gate at the top of the stairs and make sure all windows and doors are locked.
Try to build healthy sleep habits, and stick to a strict bedtime routine.
Don't panic! Night terrors are NOT a sign of psychological distress. If they are concerning you however, speak to your GP for advice.