My grandmother sleeps all the time. Is there something going on?

My grandmother is 75 year old woman who has advancing diabetes (in which she does not take care of), arthritis. And has survived from breast and ovarian cancer. She's never aware when she falls sleep. Even during conversation.She constantly is sleeping while speak to people or just while doing a normal routine. She her self is not aware of it happening. Sometimes she is sleeping the whole day.She has complain of feeling weak; whether it's to cold or to warm (when it's not); and when she tries to sleep, has a hard time staying to sleep. She is quite stubborn and does not listen to advice.

is she constantly falling asleep because some of her lack of sleep days or is there more to it?