It gets better over time, in my experience. I still can't take Epsom, it's too strong for me and definitely makes me sick, so I do alternatives. But the OO/GFJ mixture used to make me sick and now only mildly nauseous, which is helped with some peppermint oil under my nose and by chewing on a little piece of ginger after drinking it. Then I keep Altoids under my pillow in case I feel queasy during the night.
My first two flushes resulted in sick sleepless nights, ending in projectile vomiting. My last two (#6 & #7) went well, mild to moderate nausea and a good night's sleep.