I used a 42" HDTV as a monitor for a few days. The video games HUD started burning into the screen so I stopped. Plus 450W tv plus 350W computer and such and there were issues with power.

Now I use 2x 11" monitors, plus 1x 15.6" monitor. A 13" monitor, and a 14" laptop. All on the same desk, some closer than others. Although most of them off most of the time (if only in power save mode). And I'm near sighted. Most of my dual monitor use is one screen plays youtube music videos and podcasts, while I use to other to do work. All those small monitors and computers combined is still < 100W's. So at least something has improved in the last 2+ decades. I have a 27" IPS display, but it's 30W's all by itself, and is otherwise mothballed / stowed. Once it starts getting cold again I'll probably pull it back out.

I used a 32inch 1080p for a long time when I used to play World Of Warcraft. It was an adjustment but I loved it. Never felt like I was hurting myself. For my age my sight is still 20/20. I don't know. Like anything else, famous last words "hasn't hurt me yet!". Maybe it will some day. Nowadays I use a 23 inch Samsung 1080p tv for my screen about 2ft away and it works just fine. I don't get headaches, or seem to get any other ill effects.

Was it a plasma TV?

It was an early adopter LED TV via walmart circa 2006-ish. Or is as it still exists and works, even after a lightning strike toasted the surge protector it was plugged into. An Asus RT-N12 lost one of it's ethernet ports from that same strike. Which I only recently replaced, and promptly bricked the RT-N12. $40-ish for 8-ish years of wifi, it had a good run.

Not everyone puts them side by side:That may be a little misleading, as this workspace has 6 displays: 4 across, 2 high, smallest 1403 cm^2, largest 2144 cm^2. All are more distant than standard or "optimum" for a single display. Rarely are more than 4 at once active. But, one does what one must.

More distance actually makes apparent quality better. More distant fonts need to be bigger. Bigger fonts (generally, depending on display density) require more pixels. More pixels make more precisely rendered fonts. And, the additional precision can be amplified by dialing up logical DPI!

The first monitor I used for long times at a University lab was the green one from Apple ][. It was a text monitor with a "High resolution" mode of something like 200X300 pixels! Similar, the orange monitor of the second Apple ][ bought by the lab 2-3 years later. Around 1989-90, the EGA and early VGA screens together with a 386 tower were much more spectacular. Later, together with my first 486 tower I used a 13-in TVM monitor with a graphics card able to deliver a much higher resolution more than 1000 px in interlaced mode (those who lived the era of CRT monitors remember this unpleasant flickering from high resolution interlaced modes). You had to be rich to afford a non flickering high resolution quality monitor and the respective graphics card. Today's technology gives a very good & stable image at 60 frames/second.

As far as I know, not every TV can be an acceptable monitor.
Computer monitors need a picture quality higher than mid & low level TVs. A monitor mostly displays steady - non moving images / text. You need a pretty sharp image, no flickering. A TV program is usually moving images. It isn't mandatory to have a very sharp image. As an example we can think to the legacy movie film: a small frame is projected over a big screen. If you enlarge every frame at the screen's size you'll see it isn't sharp at all. However, when you see the projected movie you don't remark.

I like sharp images on my computer monitor but I don't like the extremely high luminous intensity for the highlights. I prefer bigger characters on screen and not too fine lines. I had problems with my eyes since my childhood (I had to wear eyeglasses since the 1st or 2nd year in the primary school). In my work's mswindows computers I tried to change the screen typefaces to 20-25% bigger size than the default ones. Fortunately, the company gave me quality monitors, as I usually do graphic-technical drawing work. Since 2009 I use a Eizo 22in monitor, not cheap at all, that isn't very stressing for the eyes. I'd like a bigger monitor, mainly because of the nature of the drawing work: you need to have on screen a good part of your drawing plus many command menus. Those who make use of photo editing software like GIMP share this opinion, I think.

As for health, I would advice to avoid extreme contrast and very high light intensity. Furthermore, I prefer to have the screen's center slightly lower than my eyes. With very big screens You have to keep the screen at a bigger distance.