My 6 yr old DS wakes usually a couple of hours or so after hes gone to bed, and runs up and down the landing screaming, when i go to him his eyes look through me and he screams loads and his body when i've tried to hold him still goes rigid and panicy, energy for a few seconds then relaxs for a few seconds then rigid.... so on for about less than 5 minutes. When i talk to him he responds appropriately at the relaxed times and incoherently when rigid/running around. What should I do?