boyfriend keeps having nightmares about me

a few nights ago my boyfriend had a series of nightmares where I was there and everything was fine and then I would just disappear, everytime he work up from each nightmare he checked to make sure I was still there and sometimes alive.

last night he dreamt we were laying in bed and I got up to get something and so he turned over to go to sleep and felt someone lay back in the bed so he thought it was me but all the sudden he felt like he couldn't move or talk and he realized it wasn't me who laid in the bed next to him. so when I was talking to him about it he said it was almost like I was getting kidnapped or taken from me and he couldn't do a thing to stop it.

can anyone help us out on figuring out why he's having all these nightmares, or why he feels this way?

side note: a few months ago I got into a really bad car accident, and he said he was never been more scared in his life about loosing someone