Lovelabs, that does sound scary. I don't have it, but since you mentioned walking down the stairs, I could make some guesses. :) (totally uneducated ones, though)
It could just be that this med has aggravated/caused muscle weakness. When I try to walk too much, I get shaky from tired muscles- and the first, and worst, place it happens is my knees. It is especially bad going down stairs, because youre knees need to be quite strong to support you as you go down.
Still scary, but IMO, not as scary as unexplained shaking.
Hopefully this ends soon!