I don't like needles (I'm a nurse and they don't bother me on other people, I just don't care for being stuck myself.) Sometimes that "buzz" after giving blood can be one of two things, 1) You are just relieved that it's over, and your endorphins kick in (this happens to me) or, 2)some people with blood conditions actually feel better when they are "drained." These conditions are rare, but include too much iron in the blood, and some people with migraines feel better after some blood is drawn, as we often have too much "stickiness" to our platelets and it feels good to get them out of our system. Either way, many people get a feeling of relief afterward, but don't look forward to the stick itself.
Or, hey, maybe you like needles, there's an entire kink genre around needle sticks. Again, the endorphin thing plays into it.