The child appears to be awake but she is not. As she is so scared she is also asleep. Generally these episodes last from 10 minutes to an hour. Children fall back asleep after the terror has passed. They do feel real fear even though they can't put their finger on what caused this extreme reaction.
Night terrors have their roots in a number of causes.
Stress plays a big role in bringing about this sleeping disorder. Being overtired and not getting sufficient sleep can bring on night terrors. Night terrors also can run in families, if you or your spouse experienced them during your childhood your child may have them too. Other causes of night terrors can be a reaction to medication, food and drink before bedtime, interruption of routine, and developmental challenges like separation anxiety, loss etc. It's helpful to know that although these events may be disturbing for you, night terrors themselves are not harmful to your child.