I was actually in this situation a few years ago, when I was in college. I was on my first date with this chick (we'd hung out a couple times previously, but it wasn't a "date" per se) and by this point I was all set to make a move, but I had an awful, awful flu, which ruled that out. But I didn't want to cancel, so beforehand I loaded up on medicine and caffeine. We actually ended up just going to the bar to have a few drinks which was nice, because I usually feel less sick if I drink a little.
We went a couple other places too, and I ended up showing her a good enough time that there was a 2nd date, and I just made the move then. We've been together for almost 3 years now, and she still laughs about it.
So my advice is to take any kind of combination of medicine, caffeine and alcohol that will allow you to be a somewhat normal human being while not killing you or forcing an ER visit, and then just let it roll. But truth is, if you're too sick to do it, you're too sick to do it.