Know how you feel oldgit, it’s such a miserable feeling. Happened to my dog Fred, last year. Absolutely fine one minute, then went downhill, to the stage where he would fall over and have horrendous nose bleeds etc. Took the poor chap to the vets and they said if he stays around much longer he’ll start to be in pain and so that made the decision for us. Poor old boy was put down that evening but he died with dignity still intact, and left us with plenty of amazing memories.
Take him to the vets, and see what they say. If it’s looking not so good, then don’t be selfish and let him go peacefully and painlessly. I’m pretty sure you don’t want your Toby in pain. Thoughts are with you bud.