Not heavy, no meds, 45 m. when i do light exercise, running biking etc., i will feel shaky and exhausted for a week. i avoid exercise b/c of it. why?

Exercise intolerance: 45 year old gentleman with past medical history of insomnia with question about exercise intolerance. You should get a full exam with your MD including a CBC, chemistry panel, lipid panel, and probably some spirometry +/- sleep study. A careful history will yield valuable information, as may your family and social history. Exercise is necessary for health but you must start gradually and increase.