a question I don't really want to ask but kinda do..

Okay so most of you know I have a 14 year old cocker spaniel, Sadie, who I got when I was 16. He is pretty much completely blind and deaf and has seemed to just go down hill especially in the last year or so. He just sleeps all the time. When he does move around he is constantly running into things. He doesn't seem to have a bit of excitement about him like he used to. He's slow to get up and down. He wants to go out a million times at night but doesn't have any accidents in the house during the day. I've not taken him back to the vet yet because I am thinking what's the point they can't really do much for him at his age and I don't really want to know if there is something more significant wrong. I haven't before considered this but now I kind of am and it scares me. I wondering if and when I should put him down. Ah just typing that freaks me out. I know I shouldn't just cause he's old but on the other hand he seems miserable and doesn't have much quailty of life. I, like everything else difficult in my life, try to block it out and just wait it out because either way it will work itself out. :(