An anemic rehearsal

Played a rehearsal this evening, mostly working the fourth movement of Beethoven 5. Not hard, but lots of midrange stuff, D's and E's above the staff, the flattest notes in my current setup, requiring a lot of effort to get close to in-tune. The dynamics are forte and fortissimo, trying to compete with the brass, so it's hard work. Today was extra-exciting, since I'd just given blood a couple hours before, so I had less hemoglobin to carry oxygen around. There were definite times I had a pounding, elevated heart rate, as my body compensated for the anemia with increased blood flow. That's certainly not usual. And once or twice I felt a touch faint, and spots in my vision. I felt glad every time a few bars rest came along. I think I played fine though, or at least, no worse than usual.