Had an iron infusion once, which didnt work well for me. They did a test on me first to see if any allergic reactions, but I felt fine. However, after 20 mins of starting the infusion I started feeling short of breath and restricted and my body started itching all over and developing hives. At the end i felt sick and puked out a little. They quickly pumped me with some sort of antidote which brought me back to normal.
The doctor then asks me if i have any respiratory issues, which was a yes as i do suffer from asthma.
Bottom line: make sure the doc has all your medical information before they do the infusion.