Mom is basically in good health, but seems to sleep an awfully lot. She sometimes reads - her kindle - until 10 PM, goes to bed by 11, but sleep 'til noon and even then needs a nap in the afternoon. When she gets up from the nap and gets moving she feels well, alert and has a good appetite. She does have osteoporosis and some osteoarthritis. Has a pace maker that "kicks in" when her heart slows to a certain rhythm. She gets regular checkup and her blood work is always perfect.
I have read that being on a Kindle or a computer until 10:00 pm will make it more difficult to fall asleep... I know, it happens to me when I night owl on the computer... then I can't fall asleep until 2a.m. or later :P
Just think of your Mom as being a 96 year old teenager who likes to sleep until noon :)