Generally speaking, Stage 3 is a weakened but alert state. At this point, they feel the pain of the tumors, and undergoing chemo sessions make them very tired and exhausted. Bones become weakened. There maybe bowel obstruction, its difficult to use the bathroom, a device maybe needed to pee. They may need more surgery to remove part of their colon or intestine, and they would have a bag permanently attached to them. Also, ascites starts to trap the lungs and the abdomen swells. Fluids start to build up making it tough to breathe. Sometimes they go to hospitals as much as they need to remove that liquid.
Stage 4, at that point, you can tell its death, the cancer really has spread almost all over, colon, appendix, heart. Lymph nodes are very swollen. Patients lose the ability to talk, their eyes enlarge and close as they feel the pain. Oxycodone and morphine basically have no effect. They can barely move. You're basically trying to carry an almost lifeless person. They are quite skinny like a skeleton. Think Steve Jobs in 2010 or 2011 when he looked so skinny and unhealthy.
At that point they probably think or say death is better than to suffer through that. When they reach a point where they are confused about time and place, they talk to themselves, or things we don't see, that's them getting ready to die.
My sister was 36, diagnosed at 32 with advanced stage 3 ovarian. It progressed to 4. She died last year.