for me, donating upwards of 4 vials gives me symptoms that are worse than day to day tiredness and dizzyness. I regularly get lightheaded and dizzy, exercise intolerance, get super pale when nauseous, dizzy or in pain- health care people are weirded out by it. Also get nosebleeds easily and regularly, bruise easily, was a baby that failed to thrive+wouldnt eat and was crazily pale. So for me when i say feel like death, im talking utterly exhausted, that seems excessive for the amount of blood taken-ie i know people lose conciousness from massive blood loss, and while my symptoms are not that extreme, the amount of blood is nothing compared to that yet i feel absolutely horrid and can sleep for days.
Combined with the asthma, even though my Hb hasnt gone below 12, i know i would be greatly effected-more so than my day to day symptoms. Curious about pressure though, mine is always a bit high- for as long as i can remember, its rarrly normal.