Sorry for your loss. I had to put one of our 18 year old cats down my self a month or so back after the wife ran over her. It was a Sunday and no place was open and she was suffering. I had to taker her into the woods.
She actually calmed down as if she knew what was coming. She let me comfort her and turned her back on me so I did not have to look her in the face. That will stay with me a long time.
Honestly, that would be my worst nightmare /
Maybe it has something to do with age; the older I get, the softer I become toward animals /