Why do imminent victims of a cardiac event feel so tired?

A state of vital exhaustion, characterised by unusual tiredness and lack of energy, increased irritability and feelings of demoralisation, has been found to be one of the precursors of myocardial infarction and other cardiac events. These feelings probably reflect decreased activity of the hypothalamic-pituitary-adrenal axis. Treatment of the conditions leading to this state of vital exhaustion might decrease the risk of a cardiac event.