My mom has been dealing with a head tremor going on 2 years now. It only occurs when she's nervous or anxious. Anyone experience this?

Which is almost all the time. Now it's gotten to a point where I could be talking to her about something funny or trivial and her head will start bobbling. It's a little disturbing and i'm getting worried. I know not all tremors are dangerous, and the stress of moving has probably exacerbated the tremor, but I feel like it needs to be checked out. I don't even know how she would fit into a MRI because of her weight.