Absent:
What you said about the physical / vocal changes that we adopt when speaking other languages is something that I have noticed too!
In French, I become higher pitched, especially at the end of sentences, while in Spanish my voice becomes more gravelly, more throaty. As for waving the arms around, when I returned to England after 8 months in Gran Canaria, for quite a while I had to sit on my hands when talking to people. It was the only way I could control them (the hands, that is, not the people!) 
No such changes yet when trying to speak Russian, though it's very early days. One thing I have discovered (sorry to stray off-topic) is that I can't drive the car and attempt to speak Russian at the same time - I find myself waiting at green lights and totally oblivious to speed limits. Not to be recommended. My brain clearly isn't big enough to do those two things at the same time, even though I never had that problem with French or Spanish.