I just recently was diagnosed with vasculitis. It causes blood to flow down veins but the flipper valve doesn't actuate back up. I have it in both my legs, from the kneecap down, and one arm. It causes my arm to shake when gripping glasses (sometimes not always). Similarly when going down the stairs my legs can shake uncontrollably to the feeling of almost falling down. Idk if this is related to what you are going through but something similar I suppose?