I donate blood fairly regularly. Not like every 6 - 8 weeks or anything crazy but more frequently than a lot of people. I've been donating since I was 16. My build and diet haven't really varied too much and I've never had any faintness or weak feeling after donating blood before. I'm ovo-lacto vegetarian, so I've had some issues with iron before, but I've been keeping up with it for a while, so that wouldn't be the problem, it was high enough to donate and everything. It's just, it's been over 24 hours since I donated and I still feel weak. I mean, the lady who set me up was kinda rough with the needle, but that would not cause me to be like this for so long after donating. I know it's a little bit paranoid, but rather safe than sorry... Is it normal for people who've never felt weak after donating blood for over 4.5 - 5 years of regular donating to have this problem all out of nowhere?
Sounds normal. Drink plenty of fluids in the meantime to replace volume and overcome this. Then take extra amounts of your protein source daily for one to three months.
Feeling faint is related to a drop in blood pressure, which can be caused by standing up suddenly after having been lying down for a while. This would happen to me when I was a teenager, I would suddenly stand up and get woozy for a few seconds. I never blacked out but once I figured out what was going on all I had to do was not jump up so quickly. I was not donating blood at the time. But you are donating blood, so you have less of it to deliver oxygen to your brain than you did before the donation. That means no sudden movements for a while as your body makes new blood cells.