I am a male, age 82 in October, had a quadruble by-pass in 2014, a stroke in 2008, was over weight back then: but have maintained a 163 lbs, and much better life style since , However, not very active because of a left knee operation that was not as successful as the right knee replacement in 2009. I find that I am always tired and can sleep at the drop of a hat, even if the chair is upside down What could be the reason for my tirednness? Thank you Ron