Are having "floaters" dangerous?

Yes, potentially: Having new or worse floaters and/or flashing lights could indicate a serious retinal condition like a retinal tear or retinal detachment. You must get examined, sooner rather than later, to rule this out.

No: No, but the incident or cause of floaters is.A posterior vitreous detachment causes floaters. This is a situation where the vitreous(jelly) of the eye detaches (not a retinal detachment), it then "crumples" up leaving dots, spots, strands of blurry vitreous; i.e. The "floater". You should have an exam to ensure the incident did not tear the retina, which could lead to a retinal detachment.