Bad Reaction to Donating Blood?

Yesterday was my school's blood drive. I gave blood for the first time last year and I was fine. I only had a bit of headache but that was it. This year I gave some and before hand I had some Famous Amos cookies and some water just to get something in me. I gave blood and my Iron was perfect and I felt fine during the process of giving blood and after. I left after I had a cookie and some water and started to walk to my locker then my class. I got to my locker and I felt dizzy. I started to the stairs and I suddenly felt really faint. I know that sometimes people faint after giving blood but I thought I just needed to sit down. By the time I got to class, I felt like I was going to pass out. My teacher said I looked pale. I a naturally pale person so I guess I got paler. I felt a little better after I sat down but then I had to go my next class. I always walk with my friend to her locker then to class because she needs her book. I got to her locker and I felt much worse than I did earlier. I had really spotted vision and I couldn't really answer her when she would talk to me. I was processing stuff really slow. I had to go back upstairs and I barely made it to my seat in class. I couldn't keep my head up and I felt cold and then hot. I had a bad hot flash and had beads of sweat on my forehead. My skin looked yellow to because I got so pale. I ended up going to the nurse and got some grape juice and some pretzels and felt somewhat better.I ended up going home because I couldn't walk from class to class without those side effects spiking back up again. The next day (today) I feel better but I feel super sluggish. I get pretty bad vertigo when I get up and I've been freezing all day. Also I'm getting out of breath from just going up the stairs and my heart is beating hard and fast. I've been eating proteins and drinking juice but I'm not feeling better. So I'm just wondering what to do. Should I be concerned? Or should I just wait it out? Replies would be much appreciated! Thank you!