Karston had night terrors once (at least once: we think most of his night-time all-or-mostly-asleep screaming is because his tummy hurts), and it was a disconcerting experience. The rule of thumb is that if when the child wakes up, the parents are more upset, it's night terrors. If the child is still scared, it was a nightmare. However, I learned a valuable secret to avoiding night terrors from Daddy's cousin Kathy whose son has more frequent night terrors. The secret is an earlier bedtime! Sure enough, Karston's night terror was when we were at a family gathering and stayed up very late (midnight!) with everyone else.