Involuntary shakiness?

I have a friend who was describing a shakiness that she has. She said it comes and goes and that it's only once or twice a week that it occurs. It's mostly in her hands, but her chest also feels sort of weightless. Her heart beat is more prominent than usual but not faster. She's blamed it on a lot of... show more I have a friend who was describing a shakiness that she has. She said it comes and goes and that it's only once or twice a week that it occurs. It's mostly in her hands, but her chest also feels sort of weightless. Her heart beat is more prominent than usual but not faster. She's blamed it on a lot of things in the past: caffeine, lack of food, lack of caffeine, fatigue, stress. But she told me that it's never the same reason. She just randomly starts shaking. It's usually only when her hands are at rest and doesn't last very long, but she's sort of scared it could be caused by something else.
And so, do you guys know what it is? Or at least have some ideas of what it could be.
And don't say "Go to a doctor" because that's just obvious. I just want to give her an idea of what to expect.
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