Drinking orange juice helps raise your blood sugar back to normal. If you are feeling woozy I have found it helps to take off as many layers a possible- a sweatshirt or a jacket will make it worse (something about veins expanding and blood pressure going down or some such). I also recommend coughing if you feel weak. When I gave blood I started seeing stars and the girl said to cough. It really works! It pumps the blood right back into your head so you don't pass out. One last thing would be hoping the person who got your blood was REALLY sick.