Thank you for your query. I would like a few clarifications. 1) how old is your mom? Is she overweight or obese? 2) Is she on any medications other than Xanax? 3) does she feel this shortness of breath even when she stands and moves about or only when she sits or lies down? 4) Does she visibly strain to breathe?or is it more of a discomfort like something is preventing her from taking a deep breath? 5) Does she breath primarily through her nose or mouth?( is she a mouth breather?) 6) has she been checked for any thyroid issues? 7)How long has this shortness of breath lasted? 8)Does she have any other health issues including allergies, bronchitis, asthma, varicose veins, anemia? 9) any digestion problems or heartburn? Given that her heart and lung are in a good condition, which is great by the way, I would like to focus on other modifiable factors for which I ve asked for the above clarifications. Being obese could put pressure on the lungs while sitting or lying down, which could prevent full expansion of lungs. Mouth breathers have problems with moisturise of the air they breathe in. if the weather is dry, it accentuates the reduced moisture content. If she has a deviated nasal septum, and a recent cold , it. oiled block her nose and cause the shortness of breath. Hiatal hernia( abdominal organs pushing through the diaphragm into the chest cavity due to a defect in the diaphragm ) could cause these symptoms. Anemia can cause shortness of breath because the body tries to deliver the required amount of oxygen to the body by increasing heart rate and oxygenation to make up for the reduced number of red blood cells or hemoglobin Certain thyroid problems can cause it too. Anxiety can cause shortness of breath too but the person usually is not relaxed during that time. they would be agitated or irritable and hyperventilating. it would be advisable to monitor when she gets it and factors associated with it like after a meal, body position, after a bowel movement, when she wakes up. also note the time of the day, frequency in which it occurs and count the rate of breathing( How many in a minute). it will help her doctor understand the situation better and treat accordingly. hope this helps. feel free to get back to us if you need any clarification. Wish you all good health