Healing request please

I think this is probably the first time I have ever posted a request on this forum.

Frankly, I am desperate right now. My dog (Salem) is 15 years old and is a big dog so that really is old. The past few months his arthiritis has really kicked in, he has been receiving multiple treatments for it. On top of this, he has had an odd skin infection/allergic reaction to one of the treatments and had a suspected lymphoma (tests came back negative but means he still has an undiagnosed condition).

Last night, he took a really bad turn for the worse, I thought he had another stroke (he made a full recovery from one 18 months ago) but it wasn't typical of a stroke and the vet is now 90% happy to rule this out. Anyway, we had an emergency appointment at the vets last night at 11pm. Fortunately, as I have some veterinary experience myself, I was allowed to bring him home after demonstrating to the vet that I could do the injections that he needed through the night.

Although he is walking much better today and his temperature is down (back at the vets at 9am this morning), things are still really touch and go over the next few days. One possibility is a rare condition that will result in euthanasia which he is being tested for on Thursday if he isn't showing substantial improvement (or tomorrow if he goes back downhill).

I've been up all night with him, in fact I've now been awake for 37 hours, I'm exhausted. Although I've put "healing request" in the title of the thread, I just want what's best for him either way but at the moment we seem to be stuck right in the middle until he either improves or worsens.

Thank you.