I try to give blood a few times every year. What's been bothering me is the feeling of weakness/dizziness/nausea right after the donation. Drinking lots of fluids afterwards (water, fruit juice, sports drinks) helped, but I continued to feel weak and tired throughout the day. Today I've decided to run an "experiment" and brought a 2-qt. bottle of homemade "sports drink" (water, pear juice, salt, sugar, mineral water with lime flavor) with me to the donation center, and sipped it while they were collecting my blood. Afterwards, I felt almost normal, with almost no weakness or dizziness; it's nearly been "just another day."