What Causes Numbness Or Tremors In Elbow While Sleeping?

My age is 59 years. MY WEIGHT IS 100KG AND HEIGHT 180CMS. AT NIGHT MY FINGERS AND ELBOW SLEEPS OR THERE IS TREMOR IN ELBOW AND SLEEP GETS DISTURBED. I AM REGULARLY TAKING BP MEDICINES. THIS PROBLEM IS EXISTING SINCE 3 YEARS. I AM NOT DIABETIC. PLEASE ADVISE ME WHAT IS THE CAUSE FOR THIS ILLNESS. B K MEDIRATTA