Per my above post, I switched from cassein to whey but had a bag of cassein left to use. I started taking the whey first thing and the cassein about 11am (both 25g) but started getting a sharp pain in my what appeared to be my kidneys.
I stopped and it has now gone away but seems there is a protein limit, at least for me, in a fasted state and using dairy.
Mercola had an article not too long ago, saying too much dairy can be acidic and task the kidneys so maybe it was that.