This reminds me of when I decided to go up from four ounces of wheat grass juice, which I tolerated well, to eight ounces over night. Lemme tell ya somethin'! Yes, I had a GB attack if you want to call it that. It's also called a cleansing reaction, or whatever you wish to call it. Those green juices are loaded with enzymes and many other factors, and cleanse heavily at higher doses.
I didn't even want to be within several feet of grass juice after that for years.
If you're getting cleansing from a tablespoon of dried grass juice then you have some problems to work on. Keep at it with low doses and flushes and eventually I think that all goes away.