Yes, I probably should have said for you to discuss how to keep better blood flow while donating. You may need more time sitting after donating, before moving around. Maybe just lowering your head a little bit will help.
BTW I read recently (this year?) that they've found that doing arm exercising provides diabetics the same good circulation in their feet as if they were doing leg exercises. I don't know, maybe you could move your non-donating arm around a bit to help?

Like I said, talk to them about this!

TC