I am A+. I used to donate a couple of times a year, and always felt faint after it. I had to lie there for about 20 minutes afterwards taking up the space. After a few years they politely told me that I might want to think about whether I wanted to come back or not. I think they were always frightened I would leave their premises and collapse in the street. I also don't think they tend to be short of A+.

They did say that my blood came out quite quickly and that could be causing the light-headedness, but I think it was probably it was just my needle phobia.