Shortness of breath: A sudden feeling that you’re breathing faster than usual, without obvious explanation, and without good effect. Worsens when you lie flat or exert yourself. Wheezing or gasping.
What it might mean: A blood clot or embolism has lodged in the lungs or chronic obstructive pulmonary disease, both very serious. Other possibilities include asthma, bronchitis, pneumonia and extreme emotional distress or anxiety.