C.D.
It could honestly be anything babies I believe have nightmares my daughter still wakes up cries, yells, and talks to herself at night and she's 18 months. My rule with her is unless she is screaming hestericly I leave her alone she fusses herself back to sleep. But we went through stages where she would get so upset we had to go get her. We descovered she was afraid of the dark, so she sleeps with a light on and most times is ok, we also put some stuffties in the bed and a pillow (only to be done when baby is plenty old enough) so if she wakes up she can play with them. Every kid is different and he is probably going through a faze where he just needs to have you cuddle him for a few and hes fine it all should pass soon. Good Luck