I'm sure that was just a coincidence, normally it's just like going to sleep, your beloved pet, would not have experienced any extra pain, don't beat yourselves up, you did the right thing.our 18 yo dog was just in the pain at the end, poor animal was crying even when putting the needle into his vein, me with my mother, both there crying holding him, he started to throw up from that liquid going to his veins:/ for me the worst was to see him in that extra pain when dying.
just got drunk with mum that evening.
Wotan