I had a different experience altogether when I put my life long buddy down. She was old and I knew that it was time. She was wetting in the house because she couldn't get up fast enough to make it out the dog door. She was blind. She was lumpy. She did nothing other than sleep. She was eating very little.
When I took her in I was relieved for her and happy to be able to do this for her. It was a bittersweet but a good decision that I have never looked back on. I knew that if I kept her alive it was for my benefit and not hers.
One piece of advice - when vets put some dogs to sleep the shot can cause brief, physical pain accompanied by yelping. If I remember correctly, this happens if the medicine goes anywhere other than the bloodstream. I could not bear that. My vet gave my little doxie an anesthetic just like he would if he were performing surgery. After that, he administered the shot that put her to sleep.
Sorry that you are facing this decision. ((HUG))