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
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.