Since he is regressing and was able to stay dry during the night, I would take him to the doctor to rule out an infection or something like that first.
I love this advice from Dr Greene and gives some great in site on to bed-wetting. http://www.drgreene.com/21_585.html
and this one:
http://www.mamashealth.com/child/bedwet.asp
I have bed-wetter (he's 7). He's never been able to hold it overnight except a a few times. I was a late bed-wetter.
We use the goodnights that look like boxers. No one knows (expect those who help take care of him) and if he stays the night with anyone else, I've let him know he can change in the bathroom. He knows how to clean himself up in the morning. I don't help him. We keep a box of wipes in the bath room that he uses. Main reason it really does help their brain train itself. Sounds silly but it does work and I do see more dry nights.
I'm on another mom website and I see parents discipling their child over this. That just breaks my heart when I hear that. Bed wetting for a normal child is nothing to be ashamed of or a child acting defiant. Using discpline can actually make the issue worse or they will try to hide it. I'm sure there a few exception where it's a physiological order, but you would see this in their everyday behavior.
I'm sure you aren't using discpline and I'm just rambling. =)
Best of luck. You can let him know he's not the only boy that has problems with this. You can share my son's story with him if you'd like. I think they feel a lone and they are the only one who does it.