What Causes Paralysis Of The Upper Body?

For the past five or six years, I have had episodes of what I can only describe as a temporary paralysis of the upper body. When these episodes come over me, I have no strength or ability to even lift my arms. I can feel when it is about to come on like you can feel a sneeze coming on. When I am fully in the grip of an episode, I can not move without great effort. My arms get very heavy and weak, and I feel something like electricity in my body, but not like a shock, more like tremors. It lasts no more than a minute or so, but afterwards I feel like I would be trembling all over if I didn t fight it.