D.M.
Seperation anxiety can rear its head at any time during toddlerhood, and can be tough. Here's what I do when it pops up. Talk to your kiddo, about what's happening. I know you're sad/scared/mad/frustrated but, Mommy will always come back. Start small to help him get over it. I would leave for 30 minutes at a time and ramp up, and give him to hold onto for you (my therapist recommended getting matching beanie babies) then, when I came back praised him for taking such good care of it.
He will be okay, but you want to make sure he knows that no matter where Mommy goes you WILL be back. So, even playing peek-a-boo at this age will be fun and helpful. Have him hide to in the mirror behind a towel and show him how he always comes back.
Involve grandparents in the process. So, have them over and when you leave the room when he fusses bounce back in and say something to ease him but, show him it's okay. 'Mommy is right here silly, see I'll always comem back!' It might take some time, but he'll get past it.
My son is 3 YO and went through something similar a few months ago and is going threw something similar today with visitation. It's awful because you just want them to be happy with everyone and everything, but sometimes fear of seperation can be s very scary thing to a little one who just isn't sure.
I remember the first time my son freaked out, he was 6 months old and it was terrible he cried for a whole hour until I got back to his Dad's house to get him. Just be patient and loving...it will be oaky.
Baby Center is a great resource.
http://www.babycenter.com/0_separation-anxiety_145.bc