My DS2 (4) has regularly woken up rfightened in the night, often he is not properly awake and can be very upset, sometimes sleep walk or wake sobbing. He has always settled back down again in a few minutes and has no recollection in the morning but it could be quite disctressing to see him so upset and has been happening a couple of times a week for ages,
Apparently nightmares can be caused by a dip in blood sugar which causes a surge of adrenelin and hence the nightmare. As he generally has tea at 5ish I have started to give DS a bowl of cereal at 7, after his bath and before bed and.......it has worked, no more nightmares! DH shared this advice with an exhausted colleague whose child regularly woke up and they have had the same success.
Thought I would share as took me ages to find out!!