Recently I went back from Catalina 10.15.2 to the latest version of High Sierra (10.13.6 with Security Update 2020-003) and all of a sudden I started to have the same symptoms which brought me to this blog two years ago: headache, nausea, dizziness, feeling of warmth, feeling that I was moving even if I was sitting still on the chair, etc.
Back in the day those symptoms appeared all of a sudden and then went away after a month of suffering, with me having done a lot of research and a lot of tests in the meantime, but not having managed to identify any specific fix. One day they were just gone, possibly because of an update ran in the background, but I really don't know exaclty what happened there.
Let's keep in mind that I was on High Sierra from Apr-2018 to Nov-2019 with no issue whatsoever except that single month in summer 2018, and then yesterday all of a sudden the latest and greatest High Sierra version gave me all those symptoms once again. The text seemed different everywhere, it seemed to have some sort of blurriness around, and just trying to read a pdf had become a very demanding and unsustainable activity all of a sudden.
When I found myself in the expert mode of the calibration menu, then I realised that it was basically a deja-vu of what had happened already two years prior, and I decided to immediately revert to a usable configation. I re-installed the latest version of Catalina, and then restored the latest time machine backup with 10.15.2 (note: I didn't try the latest Catalina since I quit at the start of user customization, so I don't know if it is as bad as the latest High Sierra).
Now the iMac is usable again, and all this to say that the issue seems more linked to software aspects rather than hardware. As such, always make sure to have a recent TM backup before updating to a different version of the latest OS, or before launching a security update on older versions, so that you can easily revert to a usable configuration if needed.
All those considerations are linked to software aspects we don't have control on, but then there are also things we have control on. This is my set-up if it can help, but there is an important dislaimer to make: recently when I was in the latest High Sierra, applying all the steps below didn't help, since we all know that the underlying problem, whatever it is, is not linked to brightness, colours, distance from the screen, etc (basically it's not linked to anything that someone who has never experienced our problem is going to suggest as a possible fix). But in a configuration where the "underlying problem" is not there, this set-up does wonders for me:
- Flux set at 5500K during the day, +
- Apple Night Mode turned on 24/7 (with the slider left in the middle), +
- Colour profile BT.709 v.2.0.0 which I got from http://www.color.org/rec709.xalter, +
- Brightness usually at three or four full squares during the day.
Using either Flux only, or the 24/7 Night Mode only, well it just doesn't work as well for me (even after moving the sliders further to the left in order to basically make the screen look warmer using a single tool).
All right the iMac has become once again usable to me, but let me tell you that this recent experience with the symptoms back at full steam was both worrysome and infuriating. Fact is, to me technology improvements should be aimed at making the consumers' life better, not at reducing costs by using software gimmicks to fake hardare achievements, with these gimmicks then having negative effects on the consumers. As a matter of fact, the old LG G2 which I use as a little tablet is still much more pleasant to read things on compared to both the iMac and the iPhone.