Flashing lights should never be ignored. They may or may not indicate a serious eye problem, however should always be checked by your eye care provider to ensure they are not an indicator of a retinal tear or detachment.
Flashes of light almost always means that there is a tugging force on your retina, which can be secondary to a common occurence known as a vitreal detachment. This is a benign condition where the jelly that fills the eye (known as the vitreous) comes loose from the back of the eye and in doing so creates some tension on the retina producing a vision stimulus that appears as flashing lights. This is typically not serious and as long as the traction on the retina is not too great, the vitreous usually detaches without consequence other than a resultant "floater" in the vision.
However, flashing lights can also indicate more serious problems, such as retinal tears or even a retinal detachment. This is when the sensory layer of the back of the eye, the retina, becomes damaged. This requires immediate attention in the form of laser, a freezing technique known as cryoplexy, or even surgical repair, to prevent vision loss. A successful repair of a retinal holes, tears or detachment is certainly possible, however is time-sensitive for best vision recovery. Always err on the side of caution when noticing flashes of lights in your vision.