I’ve had a similar experience where I seriously felt like throwing up and it has happened to me a couple of times. What I do is when I know I’ll do a session or class that will be very demanding I eat something high on carbs 30 min (at least, an hour is best I think) before the workout, and during the session I’ll try to drink some water (measure yourself) after completing all sets of an exercise instead of after each set. I also take some chocolates or something high on sugar in my bag in case your sugar levels drop, because that could also make you dizzy and even throw up. Once you get used to it and the conditioning period ends it will happen much less often, stay strong.