I signed a DNR when I was diagnosed with cancer. I worked as a Paramedic for a long time. I just choose personally to not go through the huge suffering if things should go bad. I had the surgery but refused the rest knowing problems for someone young having major poisons pumped into their body. I was fortunate and didn’t have to use the DNR and surgery seems to have worked well for the time being, aside from some disability.
My family was understanding but I have always been open about my beliefs and desires about major illness and DNR with them. I’d suggest a frank conversation with those you love. Expect that someone won’t understand but also know your life is yours and not anyone else’s.
It helps me not drop my toothbrush in there in our tiny bathroom though.