Not to alarm you, but I suffered the same for several years. In my case, my failure to take action may have contributed to my having a stroke.
Unknown to me, I had a quite common defect in my heart called a PFO whereby blood could pass within the heart from the un-oxygenated side to the oxygenated side. The leak was at it’s greatest when the heart was working hardest. My heart enlarged to compensate and this led to an even greater rate of leakage. I was starving my brain of oxygen and the area of my brain which was affected first was the area which processes information from the eyes. After very hard exercise (100% effort) I would have blurred vision and blind spots for several hours, often accompanied by a head ache.
One time after a mountain bike race, it was particularly bad – I was tripping over things due to a blind spot. The vision never recovered. The oxygen starvation had caused permanent damage.
I went to an optician who saw quickly that the blind spot was in both eyes (I had thought just one eye) and hence it was a brain injury. I had other symptoms and spent a lot of time in hospital and recovery. The PFO was closed with an implant inserted through an artery and other than the vision damage (which my brain does a decent job in compensating) I am back to normal.
Worth getting checked out.