I some time see fireflies in my vision they last only for some second . is it normal or i have some problem. my vision is 6/6?

Seeing occasional flashes ,like fireflies may not mean anything serious ,but i they become frequent or happen suddenly, with blurring of vision , severe headache or after a blow to the head ,it should be checked out .The common reason for these flashes,more frequent as you age, is the movement of the vitreous gel in front of the retina ,which causes the retina to send light signals to the brain.