Hello and thanks for your question. Despite not seeing any floaters first, this still sounds like traction on the retina producing the flashing. Because this can potentially lead to a blinding problem (retinal detachment) I would recommend that you go ahead and see an eye doctor about as soon as you are able. The retina is at risk for holes/breaks/tears in it from this tractional process and may already have had this happen. Once a tear happens in the retina, fluid can get under the retina and detach it from the back wall of the eye which can take your vision permanently. I know that you don't have insurance, but there really isn't a "safe" duration of time to be able to wait to see if it goes away. It very well my resolve on its own without any problem, but there is no way to predict that everything is fine with the retina and that it will resolve without consequence; therefore, the exam by the eye doctor is important.
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My opinion is solely informative and does not constitute a formal medical opinion or recommendation. For a formal medical opinion and/or recommendation you must be examined by your doctor.