I gave blood once a few years ago, but haven't done since. I was unable to give the full amount because I felt dizzy and started getting really confused about what was happening. They had to put a blue screen around me and I remember panicking and begging them to go get my boyfriend who had finished donating and was waiting for me. All I could tell them was "he's ginger," so they spent ages looking for him in the waiting area.
It wasn't a good experience, but it doesn't mean I won't give blood again. I will make sure next time I go on a full stomach and prepare myself more. I have been thinking about it more and more recently, but can't at the moment due to being pregnant.