Sounds like a night terror. They are really quite distressing to watch. Our DD would not respond to us at all & trying to calm her down made them longer and worse. In the end we would just sit quietly near her and just watch her to make sure she didn't hurt herself (by falling over/knocking into walls). One thing that seemed to trigger them (could have been a coincidence) was BBQ Sakatas (probably due to the colourings/preservatives) so we avoided them and anything like that and tiredness. When she was very tired they would come on. Unfortunately we had the odd one still and it was just her becoming older that they stopped (She is 6 now)