Hello dear... Though headache can be attributed as a side effect of Metronidazole intake, it is very less frequently seen & mostly non-serious. The symptoms as mentioned in your post may be due to either due to fluctuations in your blood pressure levels (Hypotension/Hypertension) or due to Hypoglycemia (decreased blood glucose levels) So...it will be better to get your blood pressure & sugar levels checked. If everything is within normal limits & symptoms still persist...it will be better to consult an Ophthalmologist & get a proper eye examination done. Wishing you a Good Health. Let me know if I need to clarify further. Thanks & take care.