Ok from an experience in my extended family
My auntie (Hermien) was diagnose with lung cancer a while ago. She was admitted to hospital for her final weeks. She was on morphine to ease the pain. Slowly, over her last week and a half the morphine dose was increase. She lapsed into a coma for 4 days. She woke up then and was able to talk to everyone. He breathing was VERY laboured. She wasn't getting enough oxygen and every breath hurt, even with the morphine. Then after a few hours she said "I'm going to sleep now and I don't want to wake up". A few hours later they really increased the morphine. That night her pulse weakened and weakened and then she died.
Had she not had the morphine treatement, she would have been in agony for another month and a half existing and being forced to live the end of her life. For 5 minutes, take a single straw and breathe through only that. It's very very hard. Now imagine that for 2 months. That's what it was like for her. I can think of no better way than to have let her die in this way.