I've donated 20 times, with breaks for pregnancy, breastfeeding and surgeries. I started donating again a couple of years ago but every time wipes me out. I feel nauseous for the rest of the day, have a day or two when I keep falling asleep no matter what I do, then another few days of feeling rough. I try to plan donations around when I'll have time to rest afterwards but it means writing off weekends and arranging WFH on days I'd normally be in the office. I've had blood tests and there's nothing wrong with me.
OTOH, it seems like a small sacrifice to help people in need of a transfusion. I have a rare blood type that's particularly helpful to people with sickle cell anaemia and I feel awful that I'm considering stopping doing something that could save their lives.