My personal experience has been that you can get too much salt for your body. I had the same symptoms as you, very dry mouth, my voice croaked when I spoke, I even got a dry hacking cough. I could not drink enough water to cover for the salt I was taking. Needs are person-specific.
Consider backing up to where you were able to handle symptoms. You may have gone past what you can handle right now. It's not a race.
The ATP CoFactors uses inositol hexaniacinate for their B3. I do not have any flushing with it, and I flush awful on regular niacin.