I first donated blood in college. We used to "compete" to see who could fill the bag first. I donated for many years, even after I was diagnosed with sero-negative rheumatoid arthritis. I always disclosed it, I wasn't on any meds for it, and they'd check the reference books and OK it. I never got a letter later saying that they couldn't use the blood and/or not to donate again.
When I started donating, the AIDS epidemic had just hit the news. They'd ask if I was donating to be tested for AIDS. I'd tell them, "No, I'm donating to get the cookies." The local blood bank served the Knotts Berry Farm cookies after we were done, and I loved them. I also often got a t-shirt because of some special blood drive going on.
I last donated more than 10 years ago. They had the drive set up in a mall in an area not being used for stores. I'd eaten before I donated, but it was warm, pushing hot, up there. I'd never had a problem at all, but as I sat up on the table after i finished, the tech turned back to me, looked at my face and said, "Lay down now." I managed to get prone without passing out, but it was close. They monitored me, put ice packs several places, and then when I was stable enough, moved me to another area to lie down longer. I was there more than an hour after I finished donating, and a few others joined me back there, complete with ice packs. It took me a couple of days to recover after that instead of a couple of hours, and I haven't donated since then.