Before starting any cleansing protocol (I consider Miracle-Mineral-Supplement cleansing) you must be sure channels are open...if you tend to be constipated then prior to using Miracle-Mineral-Supplement you should get your bowels loose and moving. Some herbal teas, such as smooth move are helpful or other Bowel Cleanse would be fine.
Also start with 1/2 drop and drink extra water to help flush the system. As for the pain of indigestion, I got that too, it will go away as your system cleans up.
I also had the dehydrated feeling when I first started Miracle-Mineral-Supplement , but on my second round I did not have that problem. I think it relates to many changes happening in the body, purges and a requirement for more than usual amounts of water.