What happened to my poor buddy?

[Eshotz]

Hi,

My best buddy died last night and the guilt is eating me alive. I'll give some back story, last week we had taken him to the vet because he was having some pain (yelping when jumping off our bed and his legs had given out when we I tried to pick him up) the vet could not locate the source of his pain, but drew some labs and found that his kidney function was slightly abnormal. Sent us home with a 2 week supply of rimadyl and we would re-evaluate. Fast forward 1 week, mojo, my dog had been clingy all day and trembling (not super alarming as he's been a nervous dog all his life. It started at 9 pm with him panting really loud and him losing his balance and running into walls. I came out to him after hearing the noise and it was like he didn't even know I was there but he seemed scared. He was panting and pacing in circles. I tried to comfort him but he wouldn't allow me to pick him up. I figured he was having a seizure so I made sure the environment was safe and put a blanket down for him and went back to bed ( I have a 5 month old baby and I was home alone at the time) he seemed to quiet and then started up again. After about 1.5 hours he started to whine which gradually turned into what I can only describe as the sound of a screaming cat. I wanted to comfort him but my daughter had woken up screaming from the noise he was making. I had to tend to her and he died shortly after. I have such immense guilt that I couldn't hold him and comfort him in his time of need (I'm not even sure he would let me) I had no way to get him care as I had no car. What happened to my sweet boy? And how do I move on from this guilt? I couldn't get those horrible images/sounds out of my head.