What Causes Sudden Dizziness And Blurry Vision In An Elderly Person?

I am a 54 year old veteran distance runner and triathlete. I am heavily involved in swimming, biking, and running and have done 38 triathlons in the last 4 years. I am a male, 5 6 151 pounds. Almost daily I am very light-headed and my vision is a bit blurry, particularly if I ve been sitting behind a desk or computer for a while and transition to outdoors to get in a vehicle, etc. or maybe after bending down to retrieve something under a car seat (dizziness). Strangely enough, these symptoms seem to subside with my exercise. Blood pressure and oxygen saturation are good (although BP used to be elevated somewhat). I take omeprazole twice daily and a Zantac at bedtime for acid reflux issues and also have taken a 5mg ambien nightly since my divorce about 4 years ago but have never had these issues with those medications. I also got checked out by a cardiologist last year and was given an all clear thumbs up. He took me off of Lisinopryl/HCTZ 20/12.5 after checking me out and having me record my pressures daily for a month. I was complaining with these same symptoms then, although it was more sporadic rather than almost daily. Again, I feel much better with my running and tri activities, but I obviously cannot do that 24/7. Thanks.