Funny you should ask this question, I've been meaning to ask a similar one for a while now.
For years now, off and on, I get an awful feeling in my chest if I am woken up suddenly, esp. if I've just drifted off to sleep. It feels like my heart is beating a million beats per second. I once wore a halter monitor to check for any heart irregularities because of it, but nothing registered. It must be tremors or spasms (if those are different things). I always check my heart rate when it happens and its normal.
Once in a while I do feel it in my arms like you mentioned, but I'm ususally so distracted by my chest feeling so weird I don't pay attention to the rest of me. Does that sound anything like what is happening with you?
Diagnosed with MS April 2006
Started Tysabri Nov. 2007