Mini seizure

I only used the title "mini seizure" because that was the diagnosis of one doctor; he prescribed medication that did not help. I am 67 years old and in good health. I have played basketball at a pretty high level for all of my life. I still play 2-3 times per week. I cannot predict the onset of my problem; it occurs only infrequently.
My symptoms only occur a the start of a game. I get a feeling of fullness in my head and during the first few minutes I feel a sensation in my brain, vision is disrupted and, while I am fully aware of what I am doing, my lower body seems to have a momentary lapse of connection to my brain ( perhaps like a boxer who gets "rubber legs" when punched in the head). Once I fell over backward for no apparent reason and suffered a fractured fibula.
I always warm up and feel good about playing; so, I don't think it's low blood presue or psychosomatic. Sometimes it goes right away (especially after I run around a bit) but sometimes I know, without being able to explain it, that I just have to quit for the day.
After numerous test it has been determined that I do not have vertigo, diabetes,or heart or vision problems.