I got really nauseous once and projectile vomited (I've done six MC's, only got that sick on one) but I think it was because I got fast and loose with the proportions of the ingredients in the lemon drink. I think I was using way too much lemon. Now I measure every drink.
The type of salt you use for the SWF (Salt-Water-Flush) is extremely important. I use Redmond's Real Salt, but I think Celtic Sea Salt is just as mild and good. I used to use regular uniodized Sea Salt and it was really nauseating. The Redmond's is pinkish and I think the Celtic is grayish. Stay away from the stark white stuff!