Perhaps you could try drinking half your brew, then drink the other half after you purge. I've found that the nausea and purging became less intense the more times I drank, maybe because a lot of the toxins that built up over the years were purged the first few times. Anyway I'm confident you'll figure it out, just trust the plants.
Also, every time is different. I've had times with no purge that only lasted 20 min, and times with intense purging which lasted 6 hours.