Hi, My Father Has A Blood Clot Inner Leg Above

Hi, My father has a blood clot inner leg above his knee since March 2015. Taking Warfarin and a high blood pressure pill and high cholesterol pill. He took a fall but got up and was ok until he said he needed a rest and got dizzy and passed out & was gasping air in a choking manner. He was given 2 rounds of CPR and came to. He went to hospital and has been checked for stroke and heart conditions CT Scans, MRI, lab work etc. as well as an upper scope of some sort, checking for cancer, and scheduled for a lower scope and more exams. So far no one knows anything. We haven't gotten any answers and I would like to know what caused him to be gasping for air when he passed out and also the doctor said his heart had shown signs of oxygen deprivation but we haven't been told why that could be & would like to know possible causes of this. Also wondering if a leg ultrasound of his blood clot would be beneficial to see if it has changed as that test has not been ordered. I understand you cannot diagnose or anything but my dad is bad at asking questions and having not been at the hospital when the doctors were there we are left with these 3 questions unanswered and he did not ask the doctors these questions I told him to ask. Any info would be greatly appreciated as to what could have caused this or what direction we should be looking towards for answers. In my mind I would like to know if the blot clot should be investigated to see if a piece moved off or something changed as this has not been done.
Thank You