Our cat was old and obviously very ill. We took him to the vet and she concurred that it was time to PTS. DH could not face it and went outside As the vet left to get the necessary drugs the cat had another fit. I picked him up and cuddled him and he died in my arms. No charge from the vet who said 'He knew it was time to go'.
Only 50% of middle age adult manage more than 1 brisk 10 min walk a month.

