My Dad Was 60 Years Old. He Passed Away This

My dad was 60 years old. He passed away this year in jan. He was travelling byvtrain from mumbai to delhi. He vomitted suddenly and then he got shortness of breath. No one understood what exactly the issue was. My mom and husband who were present wt him that day thought it might be due to exertion. Then when he was unconscious, they took him to hospital,however, till that time he was declared dead. Reason told by doc was cardiac arrest. He had high bp since few years and he was irregular in taking his bp medicines. Plz i want to know the reason why this happened i have no answer.