Air hunger on and off everyday gets bad, not anxiety. Echocardiogram ok, not asthma, exercise doesnt make worse. Pulse oximter 96-99% Thyroid ok. FBC K?

D-dimer? You need a d-dimer and if elevated, a high resolution CT to rule out pulmonary embolism. You need a metabolic profile (blood work) to rule out metabolic acidosis. I would also get pulmonary function tests with methacholine challenge to rule out occult or inducible asthma. If all is negative, a blood gas during symptoms would be helpful to prove hyperventilation. Rebreathing into a paper bag helps.