Yes, I have donated blood a few times. There is a difference, but your body gets more used to giving plasma after a few times. First off, make sure you always eat a good meal before you give plasma. The only time I have ever felt lightheaded right afterwards was one time that I didn't eat before I gave, and that was a long time ago on one of my first donations so I wasn't totally used to it either.
With plasma, they do put the platelets back into your bloodstream (I don't know if this was already obvious), so it's different in that respect. But I do feel like it's more taxing on your body. I usually feel at least a little tired a few hours after giving plasma.
Anyway, in summary, you should be fine as long as you eat something beforehand. One other thing is that the needle is bigger with plasma. It seriously seems like it's the same circumference as a coffee straw to me. I don't want to freak you out or anything, but if I remember the regular blood needles correctly, the plasma needle is wider. It's really not bad though even the first time. Then, once you get more used to it, it's just routine and you hardly notice it.