That does sound very scary and worth talking to a doctor about, but it's worth mentioning that our brains are hard-wired to try to fill in the gaps of our understanding of the world around us. If you are having odd visual experiences, especially fleeting ones in the periphery of your vision, it's possible that you may be experiencing something as simple as a decline in your vision and your brain is getting creative to compensate. If you have any substance abuse issues or take a medication of any kind, that could also be a factor.

I hope you are able to find some peace of mind - best of luck!