No, I'm not a doctor, yet. I have 8 exams left to become one (being mother of one and taking care of house and family, keeps me away from that goal

)
I'm glad you find primidone very helpful, actually, is a first line of treatment for essential tremor.
Also, some clinical reports give informations that primidone with lithium has great beneficial effects for bipolar patients (when lithium has effect only on manic symptoms, primidone has been found as very helpful antidepressant)
Anticonvulsants, like primidone can either enhance or disrupt sleep. They have been used as sleep promoting agents, decreasing the time needed to fall asleep (also, decreasing the amount of REM sleep) Probably, decreased REM sleep is the reason you have less frequent nightmares, because, nightmares occur exclusively during REM sleep.
Have you been informed that because of primidone use, your CBC count and chemistry panel should be checked every 6 months?