My mother ia 52yrs. while she sleeping when she heard some noise she wake up and her heart beat fast . what happen?

Brain sensitiviy: The auditory sense is the only one that remains active in sleep. Your mother has unusual sensitivity that produces an alarm reaction. The commonest cause is sugar in the diet because it induces vitamin b deficiency. If it applies, strop sugar in all its forms and get a supplement of b complex + mafgnesium + multivitamin from the health food store.

Adrenalin discharge: We have small glands on top of our kidneys called adrenal glands. These glands secrete adrenalin. Adrenalin causes our hearts to beat faster and harder. If we are suddenly startled, frightened or become angry, this discharge of Adrenalin prepares us for the ensuing moments. This is called the 'fight or flight' response. It is a normal consequence of being suddenly awakened. No harm here.