Hopefully this wont be too long winded, but well see...
I have been diagnosed with a seizure disorder since I was 12 ish. Been in the MRI box few times, hooked to the EEG a few times for short tests and even for week long tests in the hospital. Sure does suck being completely mobile and healthy on a beautiful day and you're tethered to 20' of cables and all you can do is go from your bed to the pooper and back for 5 days while watching 30 channels of TV eating horrible food which requires you to visit the bathroom after each meal. I was constantly on video too so after maybe 5 mins doing my thing they come looking wondering where I am...
Anywho. After all the tests, and two different neurologists, they still don't 'really' know whats wrong with me. Every test comes up perfect.
My 'episodes' are always my right arm and into my back, never the left arm. Sometimes one or the other on the legs, but that's not often anymore. I started with full seizures while leaving REM sleep in the early AM. Awake the whole time, fully conscious, usually 30 seconds to a minute or two at a time. Crying for my mommy because of the pain afterwards. I haven't had a full seizure in over a year now and before that one it had been at least 5 or 6 years. Even at the age of 22 during my last one, I still cried for mommy, worst pain I have ever known. My compressed disk doesn't even come close...
What caught my attention about your post was the amount of similar movements your 'spasms' make you do that my 'seizures' or 'episodes' do to me. While I don't involuntarily swing for my doctor, I do get twitching and my arms tends to go behind me, sometimes even rolling me over in bed. My problem has progressed from early AM, to include early stages of sleep (like within 20-30 mins of falling asleep) to now include episodes in the mid day for what seems like no reason. I still drive and work with no problems, I have full control of all my other limbs, and so far driving and walking while having a small episode has been OK, but it still does scare me. One thing I have noticed bring these on is certain uses of the muscles in my arms or back. Like carrying something awkwardly heavy, or something for long distances, etc. It doesn't happen all the time, but it has twice moving furniture, and a few times carrying steel to the scrap bin at work.
I am on some new meds as of the last few months which are working great. The things I have come to notice that helps the most is less caffeine, staying focused or busy on projects that I like doing, and just generally trying to have a good outlook on every situation whether its good or bad and using that to help keep my stress level as low as possible. When work or my upcoming marriage bothers me I tend to have more issues more common.
Believe it or not, my chiropractor has actually talked to me (and made the most sense on a theory) about certain parts of the nervous system which can cause problems like this. He suggested making sure I have a good calcium intake and some other things I will work on depending how my problem progresses during my buildup of my new drug and phase out of the old.
Be glad your MRI people liked you and cared if you had metal in your body. I found out I had a sliver in my hand after my most recent scan last year. Hurt pretty bad coming back out of the skin!
Best of luck and keep updating. It at least make me feel better knowing there's someone out there who knows what I'm going through.
Jason