Not everyone needs 8 hours of sleep.
In fact it is common for people over the ages of 50/60 to need LESS sleep then before . 4 hours being a healthy , normal amount for some people.
Your mom is not old by the way.
But she is starting to age in the ways that make your concerns valid.
But, when someone is not getting enough sleep, they will be tired, cranky, and you will see drastic changes in mood and sometimes memory.
Sleep apnea is a sleep disorder that causes people to wake up in the middle of normal sleep because they are not getting enough oxygen.
Their body slows down the breathing process, sometimes through the airways ( snoring being a sign in some cases of apnea) .
Other times, thier bodies just slow down the breathing process TOO much and one looses oxygen.
Most people wake during these episodes to regain their breathing patterns. Some do not.
Only sleeping 3 or 4 hours is not always a sign of apnea..
As for the possibility of stroke / heart attack...
well.. the age old suggestion works best.
Diet and exercize.
Major diet changes can be extreme on ANY ONE espically older people.
( when I say older people , I mean 60+ )
All changes should be made gradually.
Start replacing one meal a day with nothing but veggies / fruits and good grains.
A meal of brown rice, lightly steamed broccoli/cauliflower , Tofu or other protien source that is low in fat/cholesterol. Watermelon, or other fruit for a dessert..