Perhaps try saving it for later? I used to split my session into three shells. Dinner would follow the first two shells, then a few hours later I'd have the leftover as a nightcap which tended to kick things back up a few notches.
Not sure why you would want to keep going at that point, because the feeling would likely intensify as you continued. Try ginger and eating in general for nausea.
Eating something at that point is your best bet, it will settle your stomach and couple hours later you can have the other shell. I always make the same amount, 2 cups and gulp it down half and half, 20 minutes apart and that's it, it hits the spot without wanting to throw up. Overdoing it makes you feel worse not better.
I sometimes get nausea after just a few shells. Not entirely sure why, but I just mix some ginger with water and chug it. Usually settles my stomach, then I can go back to drinking Kava.