I use KDE Plasma on Arch. Today, I installed the following packages to build an AUR package and within seconds I started experiencing the dizziness and brain fog I used to get earlier:
Most likely after installing gcc, make, and pkgconf.
I suspected this earlier and that is the reason I use a separate machine to build packages (which is temporarily not available today). I uninstalled them after the package build and I am back to normal.
Similarly I get relief when I uninstall networkmanager. (I used wpa_supplicant and dhcpcd to connect to wifi).
The point I want to make is that: In addition to PWM, dithering, graphics drivers, etc, the other innocuously looking packages could also be a source of strain. So, keeping the system with minimal packages is generally a good idea, till we get an objective handle on what causes strain.
Hope this is useful.