Turns out it wasn't just my romantically undernourished student ways that made me all woozy when I last tried to give blood, I just need all of my blood at all times :-/
Even as a responsible grown up person who has three proper meals and about 2 litres of water a day, I got halfway through and all of a sudden my temperature went up, my blood pressure went down and it felt like the space between my eyes was filling up with rushing air.
The nurse taking the donation was on to things like a shot, all I had to say was "Um, I'm feeling a little..." and the needle was out, the bandage was on, I had a damp cloth on my head, a cup of water in my hand and was being fanned with a clipboard whilst she reminded me to take deep breaths and asked how I was feeling.
"Some people just shouldn't give blood, love," she told me sympathetically.
It's really annoying because being a fairly healthy and robust person I always figured I'd be able to spare a bit of my life sauce but take any more than is necessary for a blood test and the system goes into emergency procedures.
The needle doesn't hurt, the process doesn't hurt, if it wasn't for the light-headedness it would be a doddle, a walk in the park.
So it looks like I won't be able to become a regular donor which is a real shame but I'm glad I tried. I'd been avoiding going back in case they told me not to come back* - yes I know that's faulty logic - but now that I know it's just the way I function I know I haven't been wasting years of potential contributions.
The day I went in the clinic received 152 donations** which will potentially save about 456 lives, they also took plasma donations which will help people with serious health issues live normal lives instead of being gravely hampered by their conditions.
This is something I want to be a part of, even if I can't give blood I can still give money and hope that others with more vigorous constitutions than mine will give it a go.
*If you have a poor reaction three times in a row you're told that you should probably cross it off your to do list as it just isn't meant to be.
**And my half a donation which I guess will help 1.5 people as well.