My toddler was potty trained...now he's not

My son, who's 3 1/2, was potty trained about 1 year ago and used to poop in the potty (more or less). Now, all of a sudden, he refuses to sit on the potty and will only poop while he's sleeping with a diaper on. We tried sticker charts, treats, etc. and that only makes him cry now. My wife and I don't want to pressure him to the point of being too psyched out to use the potty, so we've stopped really trying to convince him to poop on the potty. However, now I'm stuck cleaning poop off him every single morning. Is this just a phase we need to let blow over? Did anyone else go through this type of regression? How many more times can I type the word poop in one paragraph? Help!