As if losing Victor wasn't hard enough... I happened to come across a channel on YouTube that posts videos of their cat, who had recently been diagnosed with diabetes, and someone mentioned in the comments that they shouldn't feed their cat tuna because it could cause mercury poisoning, which instantly resonated with me because tuna was pretty much the only thing Victor would eat in the few weeks leading up to when he got sick and we had to make the decision to put him to sleep on the 22nd of December. So I looked up mercury poisoning in cats and felt like I'd just been punched in the chest when it said symptoms were "loss of coordination and balance, and difficulty walking," which describes Victor's condition exactly when we took him into the vet on the 22nd. It also said that mercury poisoning isn't common in cats so it may not be something a veterinarian suspects. I know there's no way to know for sure at this point, but just felt like it was something I wanted to get your guys' opinions on, as the thought that we might have unintentionally caused what happened to him absolutely kills me inside.