My heart sometimes races when I am lying in bed going to sleep. I am 52 years old, female, 6' ft tall 174 lbs, don't drink alcohol, light social smoker, and I also have multiple sclerosis which I take interferon injections for once a week. I am not in a wheel chair and have a moderate level of exercise. I was wondering what could be causing my heart to race sometimes. I do not have high bp or high cholesterol and am post menopausal