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They look like floaters to me. Sometimes whe there is a pull of vitreous on the retina like when you lift weights or something, you can see them. It is not a cause of concern. However, to be absolutely sure that retina is fine you can get a fundus examination done by seeing an ophthalmologist. Floaters can be caused by retinal tear also. So, you should get it checked but most likely everything would be fine. Thanks.
Low blood pressure is unlikely to cause this but yes anxiety can definitely cause it. Infact at your age, anxiety would be on top of my list. Thanks.
It is unlikely to be anything serious though to ensure that an examination is required. I hope you understand. You can wait till such an episode occurs again. If it does not, forget it. Thanks.