M.S.
I have to second separation anxiety! I never realized it before reading Megan's post, but both of my kids did this exactly as you are describing. I just went in and comforted them for a few minutes and put them down again. Sometimes I had to go in a couple of times, but it just went away. I didn't really notice how long it took though! It is all gone now, so it doesn't become part of the regular long term routine. Good luck mama!