The cause of flashes may be more easily identified if other symptoms exist (such as feeling unusually cold or having aching limbs). I presume these are �flashes� and not �floaters�?
If they are flashes then you should see an eye specialist because of the risk of the severe retinal detachment, which in extreme cases can cause vision loss. However, other causes of flashes (and floaters) are more common than retinal detachment, such as vitreous detachment due to aging. Are you knocking on a bit?
Flashes are generally caused by improper stimulation of the eye's retina, or the optic nerve, which the brain interprets as light. Flashes may occur on movement of the eye, such as in vitreous detachment where the vitreous is pulling on the retina and eye movement exacerbates the effect. Either that or you have forgotten to take off your novelty flashing glasses after the Christmas party.
In any event, with any long lasting (i.e. 24 hours) or re-occurring eye problems should be seen to by a specialist, if only for reassurance. Better to be safe than sorry.