More than likely it is. Back of the dose and see if it goes away. The twitching is probably from magnesium or potassium loss. Up dose of magnesium (use magnesium chloride) and try some potassium or increase dietary levels.
It is possible that the vit c is detoxing and may be mobilizing toxins out of your system thus raising your metabolic rate which in turn would deplete electrolytes (mag/potassium etc. )