I donated blood the other week to try to lower my high Ferritin. Got the normal pint taken out.
I felt a little weakish after, but I had it done at probably the wrong time of the day for me since it was when my cortisol was elevated, so I think my weakish feeling afterward was mostly all the anxiety of doing it and the worry that my blood Sugar would drop during and after, but my Sugar never seemed to drop. I did bring food and ate right away after.
I did feel this weird weak feeling hours after for a couple hours, but by evening it faded. Next day I was fine.
I swear the next day when I went a very short easy jog, the tightness/crampy feel of being out of shape I usually feel around my heart and stomach seemed to have greatly diminished after donating blood.
I plan to donate blood again at the end of June, the soonest I can donate again. I've read a lot of health benefits of donating blood (bloodletting), especially for men, who tend to be higher in iron than women, since women menstruate monthly.