hi my wife has been suffering from the past 2 years for unknown reasons heart palpitation and feeling lack of breathing and like something sitting on her chest, this is random for no reasons and it happens twice a week. we saw heart doctors and after many checks it was nothing, we saw internal doctor to check her stomach and nothing was wrong, we did medical test, chest xrays and nothing wrong. we are confused and the only thing that helps is xanax to calm her down during those incedents. can you please explain if possible why it happens, the causes and what could be done or doctors specialized in this area. she is in good health, excersise at least 2 hours a day, eats healthy foods, no depression. just lately she feels worried about kids studying outside, some normal mom worries, she is happy in life, jokes, has fun, but for no reason this happens and it is not helping her life and she gets worried that this will cause her heart attack, etc and it only gets better after 10 mg of xanax.