It's a great practice, one I have done for years. I wouldn't advise strenuous activity on the day of your draw. Be prepared for giving by boosting your iron if you can. There are foods you can eat leading up to a draw. Women often have trouble meeting the minimum level required-I do. One or two times my iron levels have left me fairly lackluster after a draw.

However, I generally feel fine afterwards when I give and usually go back to activities the next day. I do agree with the other poster, that if anyone is not going to feel fine it's probably a thin/smaller person with less sturdy constitution.