I had been doing relatively well with my 2015 Lenovo Ideapad 100S for years -- not without problems, but I have tolerated it much better than most other devices dating from that time up to the present. It runs Windows 10 home 1607 (quite an old version). and I have updates turned off.
A few weeks ago I began tolerating it less well, getting symptoms (my screen symptoms are brain fog and fatigue) that I didn't used to get before so readily. I have been searching for the cause, and have come to the conclusion that it can only be: 1) A possible worsening of my vision, requiring my eyes to focus more, 2) Dry eyes due to the winter (but eyedrops for dry eyes have been of only limited help), or 3) Has Windows secretly updated part of my system without updating the entire Windows version?
Around the time I started experiencing a worsening of symptoms, I had cleared out a significant amount of my hard drive space. Before, the free space had varied between 100 or 200 or so MB and around a gigabyte. This would not have been enough to do a full Windows update anyway, even if I had wanted to. After clearing out the hard drive space, I believe it was up to around 1.8 GB (from memory).
The strange thing is that that free space has since mostly disappeared, without my having filled it up with anything. The free space is now down to 257 MB.
Does Windows do partial updates even when the Windows updates are expressly turned off? Has it possibly done some update that has fiddled with the graphics parameters of my system?