Well, one thing I can say forsure is, try not to smoke if you have any underlying issues. This might have been the reason why you had a bad journey. I dont think its bad to mix the xtals with changa, but when trying new smoking tek's its best to go one step at a time.
Try and elliminate any problems, so just smoke the changa on its own for a few times, then start mixing and trying new combos.
I never lay down when on a journey, I have gone through the same nauseas feeling with enhanced leaf, and now I never lay down, always sitting upright.
I do feel that the caapi changa is alot more earthly. Also these days, I try not to open my eyes when journey'g, I find that things get to wild for me and thats when the vomit follows, I always close my eyes, thats where the fun happens-behind closed eyes.
As I said, I always dose 100mg of 1:1 ratio changa. Maybe next time dont mix xtals with the changa and maybe not predose with caapi either. Just load up the changa and blastoff, also try upping your dose.
Hope you have better times with your changa, if not, just go back to the xtals.
Keep us informed.