my left arm is shaky too and i've asked my doctor about it like 5 times and she says it's probably just an essential tremor or i'm just weak because i don't work out lol. it's more annoying than anything, i just try to forget about it. my mom is shaky too, so is one of my grandmas. my other grandma actually does have parkinsons and it's noticeably different. i'm sure it's because you're nervous which is kicking your sympathetic nervous system into gear.