H.L.
I was a bedwetter sporatically into my 20s. I was and still am sometimes a deep sleeper. My 14-year-old (step)son sleeps really hard and sometimes wets the bed. Once you rule out any physical problems, he should have some psychological therapy. Even adults sometimes revert to this in the face of certain stressors. Don't let him drink anything but water after a certain point in the evening, and not too much of that; empty his bladder just before bed. Also, he might be such a sound sleeper because he's not getting the right amount or type of rest. (At a certain time in the evening, have him relax and wind down into sleep, instead of just falling off to sleep. Make it early enough where he can wake up naturally in the morning, or wake him gently. It's just so jarring to wake to an alarm clock or someone yelling at you that your psyche is traumatized, and you can't truly relax in anticipation of that alert.) After that, don't make a big deal of it with him. It'll make things worse if he's embarrassed. Before sleepovers, my mother would talk with the parent(s), and they'd make sure that I slept on my own bedding (alone and not on the sofa) and would wake me at night and/or get me up first in the morning so I could "freshen up" before the rest of the group. Get him a plastic cover for his mattress, and make sure that he knows how to operate the laundry equipment. Make him responsible for cleaning it up, and then leave it alone. It'll wear off. I hope that this helps.
I'm in my 30s now and have dreamt of going to the toilet while sleeping with my husband. Yep, you guessed it--I'd have to wake him during the night and fix him a bed somewhere else and remove and wash our sheets. It happens. Treat it like it's just one of those things, and it'll bring less and less anxiety.