I'm passionate about scuba diving, but it is really important to be hydrated on a dive, so as to avoid decompression illness. The last time I had a chance to dive I couldn't shake the thirst, and so I didn't go...
Now I have discovered I have SjS. I am wondering if the dryness and thirst I feel is actual dehydration, or if it just feels like it.
Must I sell my gear?
The dryness of SjS isn't necessarily a reflection of systemic dehydration...it's caused by failure of the salivary and lachrymal glands to produce saliva and tears respectively. Of course dehydration can make it worse, but generally speaking it doesn't mean you are lacking body fluids.
There are other indicators of hydration that you could use to determine that your hydration is adequate to prevent decompression problems...adequate urine, light lemon yellow and not dark yellow; no wrinkling or pruning of the finger tips; no prolonged "tenting" of the skin when you pinch up a bit on the back of your hand; and I'm sure your diving instruction basics will have others.
If I remember correctly (and there's absolutely no guarantee of that) one of our members is a diver, I'm sure he'll be along to respond with more personal and accurate information about diving and SjS.