Hello, I wanted to post an update because when I searched for info on his behavior I saw maybe one other post talking about similar behavior but no answers so hopefully this can help someone in the future. 

About a week ago I posted about my boy Sampson laying on his back a lot, including finding him on his back with poop coming out of him. I though it might have something to do with his uvb being due to be changed. It never looked like he was falling off of anything and he was moving around mostly normally. I changed his bulb and continued to monitor him. I watched him flip over at one point, he went to take a step and his arm jerked behind him and he flung himself onto his back. His back legs were also not moving as well as his front but were still responding to stimulus a little bit.

I took him to the vet and here's what was going on: due to his light being out for an unknown amount of time (I had been checking his buld with a uvb test card, not knowing those are NOT accurate) his lack of calcium was making his muscles spasm causing the behavior I saw. Additionally, the stress on his system from this caused a parasite that is naturally occurring in most bearded dragons to reach unhealthy levels causing diarrhea. He has been put on an anti parasitic once a day and a liquid calcium supplement twice a day.  His calcium levels were actually elevated which the vet thinks is due to him producing eggs (he layed once 2 years ago, see my comment on my other post about his pronouns. Tldr he's a very dumb Boi and doesn't know what gender is or care) so if he doesn't improve we were told to take him back in a week for an ultrasound to look at the eggs. The vet did a very thorough exam and determined he was not egg bound which was a relief. So far he's been steadily improving!! It's been 3 days and he hasn't flipped over and his back legs are responding more and he's holding himself up a bit more off the ground. In two weeks we take him to his follow up as long as he continues to improve. 

Things I've learned and a few notes:

Most importantly DO NOT TRUST UVB TEST CARDS I thought the conitued positive readings on my bulb were a case of capitalism making you buy things before you need them and that the bulbs last longer than a year they just only garuntee one year. Boy howdy would it have been cheaper to just buy an new bulb when the year was up, but alas, you can't know what you don't know. 

If I give him calcium powder he hunger strikes for several days, he's been fine all these years until now but if the liquid supplement isn't too expensive I'm planning on asking to get it so I can give it to him once a week especially if he continues to lay eggs every few years. 

I still don't trust him with sand as a whole enclosure substrate. I think he will eat it and while he always has good urates I would rather not risk impaction. I am planning on taking some sand from my yard and pasturizing it in the oven and giving him a sand box in one side of his tank and seeing how he does with that. I live in the desert so i figure our sand is similar to Australias lol

To everyone against using reptile carpet. The vet had zero concerns about his substrate. In fact he thought it was good that I could just throw it in the wash once he's done with his antiparasitic. Also in six years he's never lost a nail or gotten caught. Also also, carpets are easy to clean as they can be put in the washing machine and uv is an incredibly effective sterilization method, it's what's used for medical equipment and water treatment. So between the washing machine and his uv lamp the mats are not a cleanliness concern. 

To those saying Sampson is overweight, the vet said he is in "perfect body condition", he did not think laying eggs was an over feeding issue. Additionally you can see his tail is not significantly plump which would be an indication of excess weight. Honestly I don't think i could get Sampson fat if I tried tbh he frequently will not eat for a few days even bugs. 

I'm including these last points not to start fights but in an effort to put accurate information out there as reptile care information is hard to find and these things have been confirmed by an incredibly good vet. Anyone in Phoenix or Tucson should consider arizona exotics their go to as the care there both times I've had to take Sampson to the vet has been extraordinary. They are very skilled, knowledgeable and really care about your animal and go above and beyond. 

I will link the previous post in the comments, I'm hoping I've put enough key words in this post that it will come up for the next person who finds themselves googleing why their bearded dragon is laying on their back and repeatedly flipping themselves over. If there's any other key words you think would be helpful please comment them 🧡

Thanks to everyone who commented on my previous post especially those informing the uvb test cards don't work. That is incredibly upsetting to learn and I hope that info becomes more widely known 

Update : laying on back/repeatedly flipping over problem