As I understand it, there are about 80 different drugs that can cause myoclonus....just for starters. I suspect that depending on where it is in the body it may have different aietiologies (causes and progressions).

Palatal myoclonus I am currently researching but have not had much luck contacting Topsie in this forum, who also seems to have it.

I understand that palatal myoclonus can be caused by some malfunction in the Guillain-Molleret triangle. The precipitating cause could be post infectious brainstem encephalitis. I have also read of a person having their palatal myoclonus cured after removal of adenoids...go figure!
Am still researching this.,

Walker its interesting you say your wife experienced this after epidural...since I recall my mother coming in to hospital to visit me after childbirth and noticing my entire body was shaking.. (BTW< my epidural only worked on half of my body and just prior to C-section incision and about to make the cut they checked if I could feel both sides, one side I couldnt ,the other I could ...then they must've topped it up. I swear I sensed an airbubble rising right up into my throat on the r side as they cut into me.

I think possibly injury, infection and medications all may play a role. Hope your wife finds some respite.
Topsie is correct that the cause involves overfiring of noeurons in the brain...but the reason could be because of some damage aeitrogenic/car accident/dental work & medications.