Post angioplasty restless, breathlesness

My father went through 2 angioplasty within 6 month- Oct'21 and Feb'22. Post angioplasty he have episodes of feeling palpitation, dizziness and breathlessness every few days. After this episodes he feels weak and dry mouth for 1-2 days. Doctor saying no heart related issue as done various test even post ops and prescribed medicine for stress release and body fluid but still get these episodes. Also consulted GP and he also prescribed medicine QVAST and BQUIT to have body settle down with stent and feel more energetic. What could be the reason and any recommendations. His BP though remains normal and Oxygen too. Sometimes BP gets low at 115/59. Doctor also suggested to increase little salt intake and take fluid.