Sue, I apologize for being late reading your thread.
I'm so saddened to read about precious Nanook. Like others here, I know it's so difficult to watch our beloved, special, heartstealing pets become ill and suffer. It's all consuming. As my Cody was getting older, and his hip dysplasia was worsening, I asked the vet also "how will I know? and his reply was simply "You'll know". I thought that was cold and heartless because I'd be the one to have to make the decision to send him to RB. Some quick cancer attacked him unexpectedly. And HE actually told me, by his eyes, that he was ready. I know he did that special gesture out of loyalty, devotion and love, to spare ME the pain of deciding for myself. I know you worship Nanook with all your heart. And that's all you can do. Take one day at a time and keep loving him as much as you do. My heart is so heavy for you. You will never ever forget Nanook. I still call Logan "Cody". I pray for both of them every day. Prayers and hugs to you during this difficult time.