My son is so sick, please send good vibes.

Just wondering if anyone has been through something like this. We started him on Gabapentin for anxiety/reactivity as we were travelling (his favourite thing to do) but had recently noticed he was more reactive than his baseline. He took it no problem, it chilled him out as intended. We noticed though that he was so so thirsty- which we celebrated at first as he is normally a dog that needs to be coaxed to drink- but then we soon noticed he was drinking like a camel and peeing A LOT. After two weeks on the meds, I took him off- but the drinking continued and he ended up wetting himself in his bed and appeared lethargic- straight to the vet- they ran blood and he has extremely high levels of calcium in hie blood and have so far ruled out Addison’s. He is now weaker than ever, struggles to walk a little and then collapses fatigued, he is twitching….. I am fearing he is DYING…… they are doing more tests right now as I type this but I fear cancer is going to come out of their mouths. I just hope there is some rare thing with this drug and these symptoms but everyone says that is not possible…. Grasping at straws. He’s still four. Just my little boy.