Restlessness and fast breathing.

My 80-year-old father has recurrent episodes of rapid breathing and restlessness, mainly in the evening after lunch and afternoon sleep. He was hospitalized previously with severe breathlessness, diagnosed with acute LVF, and underwent coronary angiography. No angioplasty or repeat bypass was advised. He had bypass surgery 20 years ago. His oxygen saturation remained 98–99% during hospitalization. He also has chronic acidity, constipation, and a history of gastritis. Dytor 10 mg, previously prescribed SOS, was restarted recently as symptoms returned. Could these episodes be cardiac, pulmonary, or gastrointestinal in origin? Why does he remain relatively normal during the first half of the day? What further tests, treatment, or medication adjustments are recommended?