It wasn't painful for my mom. She developed a lung infection that she was too weak to fight off. She was put on morphine to ease her breathing anxiety about a week before she died. Morphine affects your ability to focus your eyes and organize your thoughts, so she wasn't able to talk much, but she was smiling and responsive to us (able to hear us and understand us) until about 24 hours before she died. The problem with leukemia is that your body eventually becomes too weak to fight off any infections, so any kind of viral or bacterial or fungal infection becomes potentially life-threatening.