Sir there is no medical condition where one gets breathlessness by inhaling there own (flatulence) gas so I am very sure its not the cause. breathlessness may be due to inhaling allergens so consult a specialist to know about things which your wife is allergic and avoid such allergens coming in contact to her, breathlessness sometime can occur if a person is anxious or nervous, people who hav suffered trauma or gone through some personal unbearable things, remebering such incidents repeatedly can also cause this so doing meditation and morning yoga helps to destress and if that's the case consulting a psychiatrist is a better option