13 year old dog - Very sick

[Macrun]

We have a lovely 13 year old retreiver mix who when I left for vacation - my husband found her on the floor in vomit unable to move. After a few hours he assisted her in going outside where he could see she had had some kind of seizure and seems partially paralyzed on one side. After two days of barely moving, eating or drinking she was on her way to be put down - I suggested Rymadil and after that she has been able to get up and wobble around. However it is hard for her to eat and drink, she is confused and wobbly and has a lot of blood in her stools. Has anyone experienced this - we feel the next trip to the vet will be the end. Are we prolonging the inevitable - she is a big dog who has lost a lot of weight and seems very old suddenly.