M.G.
Mine did this. I wouldn't be alarmed. I think it's pretty common for babies to just stop doing something they've mastered - usually before they are about to tackle something new. Sometimes they lose interest too - only to pick it up again in a few weeks. That happened to us a lot.
A pediatrician would know if something were up. I wouldn't go booking an appointment with a neurologist at this point :)
I had walkers, who would decide they were done with walking, crawlers who decided they could only go backwards (after having crawled forward for weeks), etc.
I know - we all worry about this stuff but I think he's fine. I have a friend who's child just never got into rolling over. He's a bright 8 year old now :)