I thought they were intention tremors, but my doctor demonstrated what one would look like. Mine are far more violent and quick, and absolutely impossible to mimic. He said they would be more accurately described as spasms than tremors, but beyond that hasn't been very interested.
But to me they are a major annoyance in my life, and besides, I want to understand what's going on.
I've looked up everything that seems similar, read up and watched videos, and haven't found anything that matches (a few seem close).
For an example: one time I was trying to hand my card to a pharmacist. Just before he could take it I had one of these very quick spasms, which resulted in my card flying across the room.
I think it happens too quickly even for the onlooker to really see what happens (in part because the two times someone has been looking at my hand when it's happened they seem utterly surprised at the result--in this case the card flying across the room), but to me it feels like my hand shakes back and forth multiple times in a fraction of a second.
It also seems to create a momentary but fairly dramatic change to my mood--a momentary depression--but I'm not sure how much of that is from the physical effect and how much is just a normal emotional reaction to the event, since I'm aware it's happening and can do nothing about it. It FEELS like there is an actual physical contribution to that emotional drop, though, even before I've quite processed what has happened.