I had the chance to restore the old HDMI cable and use the old setup for four weeks, while no one was around. After some adjustment due to the hostile environment (very bright yellow-blue LED overhead lamps, which could illuminate a football field, in the line-of-sight of the display), I could reach the end of the day with minor discomfort. Definitely, no memory effects once leaving the room.
Then, things turned to the worst. The upgrade of the working station resumed and was completed, including plugging in the new fancy HDMI cable. I immediately felt my neck and shoulders tensing, and eyestrain developing. I insisted and after 2-3 days I would exit the room devastated at the end of the day, like, I once went to a movie theatre at night and I had to leave. I could not watch the movie. I described my symptoms more in details in the thread dedicated to using the eye patch, since I did try to use the eye patch to alleviate my symptoms. Coupled with little sleep, using the eye patch turned out to be suicidal.
Back to the display and what I perceive, the problem seems to be that the white background glows inhomogeneously with the new HDMI cable. I am not sure if flickering is the right term, but it is like I can see all the white pixels glowing distinctly, and this affects either my eyes or my brain. I decided to not avoid the problem and to carry through. The situation has not worsened luckily. After a week, the level of discomfort seems to have come slightly down from its peak and have plateaued. However, it is still bad and I am not confident it will ever get to an acceptable level. My daily life is still badly affected. Besides the eye and neck and shoulder pain, I feel really tired and deprived of energy at the end of the day.
I am not an hardware expert and I trust what you guys wrote regarding HDMI cables. Yet, my symptoms are real. They go away if I put the old HDMI cable back, and they return if I use the new cable. Now, can it simply be a bad cable?