It could be a phase, or anxiety over the coming changes, but it could also very well be a medical concern. I would keep an eye on him the next few days, try not to "play into" him doing it. If it doesnt stop in a few days I would see a dr -- if not before. Its better to see the Dr than wait and have it be something bad.
Have you asked him if he needs to see the Dr? Or maybe just tell him maybe we need to see the Dr or go to the Hospital. If he is "faking" he will stop immediately. If he isnt, then you should know. My kids will stop instantly if I mention the dr or hospital.
My Daughter used to make herself sick every night at bed time -- all over her bed YUCK. Well, I got sick of cleaning that really quick, so the one night I told her if she did it again she had to clean it. Apparently she didnt believe me -- but after making her clean it once, she never did it again. I know not quite the same, but just thought I would share that kids do strange things for no good reason!