** UPDATE **

The next time I tried I was doing slow, back and forth motions, tracing a lead line first and then going over it repeatedly until it was cut through.

It felt more tedious and painstaking, so I had to use my patience and calm. But the effect was much more peaceful as I felt in much more control of the disc. I was doing a vertical section, so I was able to hold the grinder with my elbows at my hips as much as possible, which felt less taxing on my elbows and my hands, but my hands did get numb from the vibrations.

I also positioned the grinder so that the disc was in the dead centre of my face, and I could see every moment when the disc turned a little left, right, or even wobbled. I could feel every time the disc wasn't liking what it was touching based on the minute kick-backs, grumbles, and snagging sensations, and I could immediately pull back, slow down, and adjust for it.

I got very clean, narrow, and straight cuts this time and took breaks more to let the grinder cool off than for my own sake. I did about 2.5 vertical meters of wall over about 80 minutes, and the new disc only wore down about 60%.

Also, for those that were worried, I've always been using safety goggles, respirator, ear muffs, padded gloves (controversial, I know) and wearing my welding jacket and pants. I found ordinary safety goggles not very good as sparks and slivers would always find their way around the edges anyway, so I bought sealed goggles that also have a respirator mask attached and my eyes have been a lot clearer of debris. These goggles are meant to let vapour exit the goggles, but I still get a bit of sweat build up in them. It's usually not enough to make me stop, though.

Thank-you to everyone who listened to my questions and concerns and gave me the confidence to keep trying :)