4 yr old regressing...won't poop in toilet

My 4 yr old has been fully potty trained for over 2 yrs now.  Just last week he has had two accidents, not making it to the toilet, and has pooped on the floor.  Now he refuses to poop in the toilet and says he is too scared to go.  He won't even sit down on it.  I'm SOOOO concerned and don't know what to do.  I don't know if it is a mental issue, or what it might be.  He doesn't eat like he used to, he won't play outside anymore, and just wants to lay on the couch.  I think it is because he feels the urge to poop when he is standing, and he doesn't want to go.  I don't know what to do.  Any suggestions?????

[lilsmamma]

Has there been any changes in the family dynamic lately? That could be why there has been the change. Has he not gone in the toilet since the two accidents? When I was potty training my daughter she refused to use the toilet and would hold it in. She became very constipated and was in physical pain. I asked her doctor what to do and she suggested milk of magnesia, the sensation became too much to ignore and I finally held her to the toilet until she pooped. For a few weeks we continued with the milk of magnesia until it became routine to go on the toilet. If it makes you feel any better, my 4 year old daughter has suddenly become scared of things too... Hope this helps and good luck.