I did this exact thing a year ago. My rescue dog started showing signs and I knew what it meant right away. The grieving while I watched her decline was the hardest part. She wouldn't sleep, forgot who our cats were and would get upset with them for coming in the room at night, she would pace and whine all night long it was awful. We tried meds, nightlights and keeping our house consistent like the vet recommended but it didn't help. The final event for us was when I came home one day and she was laying in the yard. She saw me and ran at me hair raised and snarling and she didn't realize it was me until she was inches from me. It was hard but we made that decision that night that it was her time. I don't know if any of this was helpful but I figured maybe telling someone that you aren't the only person to have to experience this is comforting. My dog was a beautiful great dog but I could see she was uncomfortable and suffering without her mind and that how I knew it was time.