I A M Approaching Eighty Years Of Age. I Am

I a m approaching eighty years of age. I am healthy in general, and still go to work every morning. I had mononucleosis at my early twenties and used to sweat at night. Since the early thirties I discovered that I was hypertensive. since I have been on medicine and healthy low salt diet, and have been feeling fine since. I am physically still active. My only problem is that I wake up at least twice at night drenched with sweat around the greater chest area, and do change my T shrts. I am curious to know what causes this uncomfortable experience....