T.P.
I have an 11 month old boy, and I have had a few instances with him where this has happen. Not sure if either one of these apply, but my son had acid reflux and we did not see the first sign of it until he was 2 months old, that would cause him to cry excessively if we laid him down after he ate. Also, I think they say 6 months is the average age for separation anxiety to start, but at 5 months my son would cry whenever I would leave the room. We co-sleep with my son still because I am a worry wart, but I imagine if I put him in a crib at that time he would of freaked out just like he did when I would leave the room. It may not hurt to ask the doctor to see what they have to say.
Good Luck :-)