Sudden Feeling On Heaviness In Stomach Followed By Loose Motions, Hot Flashes, Unconsciousness. Has Stent Placed Post Angiography. Cause?

Hi Doc, My father got operated in May for heart . He had an angiography and then stent placement. Since then he was fine following the instructions provided by doctor. But today afternoon he suddenly felt heavyness on stomach area and then he went to washroom. He had very bad loose motion which continued for sometime. After that he sat in sunlight to take some rest. However, after sometime he started feeling very hot from inside and he just took off his inner and shirt as if the heat was unressistable for him. After that he went in shadow and sat quietly for sometime. He felt as if he will vomit . But in a very short span of time he suddenly fell down and got unconcious. He was sweating very hard and these were cold sweats. After 10-15 mins, he came back in senses, but was not able to speak properly for another 15 mins. Please let me what can be the problem? He is dedicately following the routine told by cardiologist but still this happened. Is it related to heart or something else. Please help me and suggest me what to do? Regards, Vipul