Recently Expired, Regular Check Ups Normal, Had Stent Placed In Angioplasty, Dr Said Thrombosis. Opinions ?

Hi doctor. My father recently expired. Am not at peace because it was a matter of seconds and the doc said its thrombosis . He had an angioplasty almost 7 yrs back with a stent due to a major heart attack. Am surprised that last month within seconds he lost consciousness and his life with no warning atall. His reports from regular check up were normal. But he used to complain of palpitations due to sudden anxiety which was appraently normal . What is ur opinion and observation here