My heart aches as I read the stories shared here of lost loved ones. It is certainly NEVER EVER easy to let go. I convey my deepest sympathy for your losses.
RJ...I do love that you have the memory of your mom shopping/preparing Thanksgiving. Sometimes, though shocking, I think these types of cancers are so devastating...It's best they go quickly. We're never prepared, but the suffering your mom would endure will be Hellish.
My mom is 88+ with a definitive DNR. However, when she went into heart failure following heart attack in 2013, I fought with the doctor to bring her through. She did great for another year. Last Valentines Day I arrived at the nursing home to find her being loaded into the ambulance (non-responsive). She was in an insulin coma. She was totally unconscious as I screamed her name and touched her face. She opened her eyes, but could say nothing. Tears rolled down her cheek, as I begged her to come back to me. The medic administered IV as we raced 15 miles to the ER. Again, the doctor (a foreigner with poor communication skills) asked me why I would want to keep an 88 year old woman alive? He asked this in front of my now-conscious mother...I then asked him to step outside, rather than talking about my mother like she couldn't hear him. I found that not only rude, but inhumane. Again, she pulled through and is back to her usual curmudgeon (meaner than a copperhead) self. That's kinda funny because we are both copper "heads". 
I guess my point is this...She's my mom, no matter how devoutly evil she is. I want her to have the best medical care that an institution can provide, because Lord knows I cannot bring her into my home and suffer the consequences. I, as her POA, definitely would never allow EXTREME measures to be taken for life support. But I also would not allow her to be denied the procedures that could bring her back to a reasonably healthy state. I question this more often than I should. I have 5 siblings of which I am the baby @ 53. However, not one of them has ever stepped up to the plate to help my mom or me. I get the hard decisions, but I fight the good fight...whether with her or for her. I DO question if I should have let her go both times. I do know that if she were in pain or suffering, unable to eat or drink to sustain, facing a terminal disease...this is JMO...I would not want to "extend" her breathing with no hope for healing.
If your mom is sleeping and non-responsive, like others have suggested...you and her medical team will have to make some tough decisions. If you are an only child, then it will be up to you if she has no DNR. I am so sorry for your mom's diagnosis. I am also sorry for your health issues, that I'm certain are compounded by this stress. I understand more than you know. You're with a great group of folks here who care. Lean on us.
Hugs~~Dixie