Jerking about in bed

Last two nights, especially last night I have been experiencing really violent body jerks, sending my head towards my chest and my legs up off the matress. Sometimes my arms fly off and I expel air (from the mouth!) in a grunt. Must have had a couple of hundred of them last night, needless to say with very little sleep. Never had anything so violent before, though there have been a couple of nights in the last few months where I experienced something much more mild and only a few times. Seeing the doc later. Anybody know if this can happen when standing on your feet or driving, as I have only experienced it in bed.