Yes, I've experienced this exact thing, and you describe it very well. It was in the late 1980s, when I was IP for two months for agonizing withdrawal from benzos (Xanax). I haven't thought about this for a VERY long time. I was profoundly fragile at the time, on a lot of meds to prevent seizures and treat mania. I was surprised and embarrassed to realize that I was making facial expressions and gestures, mouthing words silently and grimacing, smiling, frowning. Yes, people looked at me strangely, but of course they were in treatment too, so they had their own problems to deal with. This behavior diminished over time (maybe 6 months), and I've never had it since.