yes, they definitely vibrate. I hadn't noticed actually until I read your post. But, after I read your message I later went to a quiet room, focused my attention, and suddenly I was aware. So, thanks for pointing that out. My creatures are really large as well but I have not yet successfully cured myself. (I can share pictures if you are curious.)
Every doctor I have asked for help refuses to even consider I am telling the truth. They all insist its just undigested food or the perhaps the lining of my stomach. I listened to them and worried I was crazy until the evidence was clear and it couldn't be anything but parasites. .