Does pain tolerance increase with dementia?

My mother has always had a very high tolerance for pain. No novocain needed at dentist no matter what they were doing, etc. She is now 86 and seems even more impervious to pain. She fell Friday night and cut her arm badly on the end of the basket handle of her rollater. She insisted she was fine despite the blood dripping on the floor and the fact that she couldn't get up. I ignored her protests and called 911. They took her to the ER where the doctor said he couldn't believe she wasn't screaming in pain. She said it didn't hurt. He applied numbing medicine anyway. Apparently the cut went almost to the bone plus several inches of torn skin. It took him an hour to sew up the inside of her arm. The skin was too thin to hold stitches. and they were unable to pull it together. Home at 2:30 am. BTW, She kept asking me why she was there. She didn't remember the fall or the ambulance. Back to urgent care Sat. because she was bleeding through the bandages (but it still didn't hurt). Only wound care appointment before next week is Thurs at 8am. That will be fun since she doesn't usually get up until 1 pm. Meanwhile, I am dealing with the bandages since the open wounds keep seeping. In addition to current situation, I'm worried about how to tell when she is ok or not ok? Is this high pain tolerance common? How do we deal with it?