It is a wonderful thing to have the time and health to share your blood with people who need it. Still, you have given up a substance vital to your body and it will need time to replenish.
Immediately After:
Do as the physicians recommend and relax around the Blood Center for up to thirty minutes after your donation. It helps if you regularly go to the same Blood Center so you get to know what they will have around for you to snack on. The worst side effects are likely to happen immediately after the donation. Your body needs some time to just out right recover from it.
The Day Of:
If you give blood in the morning, expect to have a more leisurely day. You will shorter on energy and will need to take more time to recover from physical activity for the next day or two. Do not donate blood then go running a marathon, that is simply a recipe for disaster.
Diet the Day of:
You want things that will encourage you to both feel good and will help your blood move along better. You will want to drink water to replenish the lost fluids and have something with iron in it. You want to feel good but also give yourself a chance to start rebuilding what was lost in the donation. This means having some salad, nuts, beans, shell fish and lots of water.
The Day After:
As noted earlier, you will have less endurance than before the donation. You will fully recover within the next day or so. Take this day closer to your full pace, but still hold back just a little to be on the safe side. If you feel incredibly energetic, then have fun.