both my parents died of dementia/alzheimers. At some point they refuse food and medications and become very difficult to arouse. They fade away quickly. In the final stages their bodies tend to stiffen, and any movement was quite painful. Both in hospice and given the order for oral morphine. It was given to keep them out of pain. It is possible it pushed them over the edge, but they were ready to pass, death rattles, etc.