I donated a kidney. The surgery was in late afternoon. In the morning when I davened שחרות I did not remember that I did not daven מעריב. I few days later I realized that I didn’t daven מעריב and was very aggravated because I could have davened two שמונה עשרה for תשלומין. Now I am thinking that since I was an עוסק במצוה פטור במצות donating a kidney it was better that I did not remember because I was פטור and could not daven an other שמונה עשרה. I am wondering if I am correct. It is important for all future donors.
WOW! Wonderful, you have the zechus that you are saving a life every minute, with your flesh and blood! What a tremendous mitzva, (and in jest I would say don’t do it again)!
Regarding your question, although donating the kidney is a big mitzva, but your involvement in the mitzva finishes, after you have already given the kidney. Therefore, from after he operation you are considered choleh, but not an osek b’mitzva. Therefore, although you were most probably an “ones”, during the night, and you couldn’t have davened, it technically would have been possible to daven a tashlumim the next morning, (if you would have had the strength for it.)
May HKB”H help you do more mitzvos and more chesed, and you should have arichas yomim.