It was the Eye Hospital that suspected and initially diagnosed the Sjögren's Syndrome, and they sent me to the Dental Hospital to confirm it.
The Dental Hospital worked out a treatment regime for the dry mouth and throat part of it. But that involved quite a few meds which my GP refused to prescribe. Patient's Advocate involved, and more. Got meds reinstalled. But then a few months down the line my GP stopped most of them again. Patient's Advocate again, meds reinstalled again, and then GP stopped them again. I was entitled to those meds according to the rules. It was never going to stop. I now am back to 2 prescription dry mouth meds. I finally gave up the constant GP battle. This was 18 years ago.
The very dry throat is why I have to sleep almost upright, otherwise there are problems breathing, because the muscles in my dry throat seize up, and then so does the airway tube because it is right next to those muscles. I needed the Prescription only dry mouth spray for that, but GP refused.
I ended up researching myself in the end for best ways to help myself. Some good friends in the States gave me several good suggestions and I had to buy stuff from the States then.
One I found very helpful was XyliMelts. I can get it on UK Amazon and eBay now.
https://www.amazon.co.uk/s?k=xylimelts+for+dry+mouth&crid=20OJSWUSVF9JF&sprefix=Xylimelts,aps,159&ref=nb_sb_ss_ts-doa-p_3_9
The thing is I need to suck something all night to stop my dry mouth going so dry it sticks together. (My eyes do the same, my eyelids stick to my eyeballs by morning, and so I am using prescription eyedrops during the night). And the XyliMelts are the safer option to suck for my mouth being much smaller. I have sucked soft pastilles when I have run out of XyliMelts. I cannot drink just water on its own, it is too dry (it's like drinking sand), and so I put a tiny bit of xylitol in the water
Some people don't like XyliMelts, but they have been a lifesaver for me, literally.
Same here about Dentist, he is still not seeing patients.