Muscle fatigue, certain medications, large intake of caffeine, hemi facial spasms, due to chronic irritation of nerves of face from tumors,
multiple sclerosis plaque, etc magnesium deficient diet etc. consult a neurologist immediately, a balanced diet, foods high in potassium, calcium and magnesium, massages to relieve physical stress and fatigue, vitamin B complex rich foods,certain drugs like gabapentin, phenytoin,carbamazepine, botulinum toxin injections. Take care.