Inside the eye is a clear gel overlying the nerve layer, the retina, which assists in maintaining normal vision and eye health. Over time parts of the gel become more liquid and can have small opacities, these can create the appearance of floaters in vision. In most cases, these are not a cause for concern and are a normal ageing change.
However if you suddenly notice floaters, experience a sudden increase in the number of floaters,  or have a patch of rising grey or blacking out, you should have your eyes examined promptly to search for any retinal tears. Also if you experience flashing lights with or without floaters you should contact your optometrist immediately, as these can be associated with the risk of a retinal tear or other causes like migraine aura.
Floaters and flashes are warning symptoms, which demand prompt examination, but most people who experience them never develop retinal damage.