There's also the chance of it being a pain reaction. Especially since you were gone so long, make sure to give him a good once-over (have fun trying to check the mouth XD ), just in case he maybe messed up a tooth during a feeding or something. I'm fostering a 5 year old male, sweet as anything and a little shy, who's never gone through that severe of an attitude change from neglect, and there's a reason I'm fostering him. I've never before seen a snake visibly relax as soon as it was away from it's house.