Breathing difficulty involves a sensation of difficult or uncomfortable breathing or a feeling of not getting enough air. No standard definition exists for difficulty breathing. Some people may feel breathless with only mild exercise (for example, climbing stairs), even though they do not have a medical condition. Others may have advanced lung disease but never feel short of breath. Wheezing is one form of breathing difficulty in which you make a high-pitched sound when you breathe out.
Dyspnea
Hypernea
Apnea
Tachypnea
Orthopnea
Labored breathing
Fatigue  
Fatigue