No pain, headache, vision changes, dizziness, weakness but during first mile of run, legs feel uncoordinated and first downhill is unbalanced feeling, all resolves as i warm up. no new med, no alcohol, age 60, running for decades. no tremor, no falls?

It is a puzzle. Personally, at age 70 I have found that what I think is initially low blood sugar at the start of exercise can result in those symptoms, which also seem to resolve as the body adjusts to exercise. I drink 8 ounces of something with sugar (iced tea) just before i start running, and I carry hard candy to take at the start of those symptoms. These seem to prevent them. Good luck!