Unfortunately, ischemia from occluded vessels is happening at a younger age. There was an article I read that stated many casualties from the war had an autopsy and it revealed that there was advanced CAD.
Condoline's suggestion to get a evaulation for an underlyig cause is good advise. Thanks for sharing. Take care and if you have any followup questions your welcome to respond.
You are describing acid reflux to a T, which often occurs while lying down where gravity no longer holds the acid in the stomach and it spills into the esophagus causing a visceral pain.
Given your age, its highly unlikely this is your heart.
As with any chest pain, the prudent advice is to always see a physician to have it assessed as the internet is the poorest of substitutes.
However, don't panic yourself over this
Chances of a heart attack in a 21 year old is almost 0. There is no possible way you suffered a heart attack from coronary artery disease or a blocked arteries. That just can not happen in someone young like yourself. It is possible for a young person to suffer heart failure or some other type of arrhythmia from genetic problems with the heart, or abnormal pathways of the heart. This would not be called a "heart attack" A heart attack is describing the situation when blood vessels that supply blood to the heart
are blocked, preventing enough oxygen from getting to the heart. The
heart muscle dies or becomes permanently damaged. Rarely do heart arrhythmia's cause pain. I have violent PVC's and NSVT and do not get any "pain": associated with it. Maybe you should go in for a holter monitor but chances are you are just fine.
Get to your ER ASAP. They can determine with a simple blood test if what is going on with your heart is a heart attack in progress or about to happen. Don't try to diagnose yourself. There are a lot of different symptoms for heart attack, and some seem pretty innocent.
As a person who had a silent heart attack I probably should not give you this advise. For 5 or 6 seconds I do not think sounds like a heart attack. But if any shortness of breath weakness or dull pains in the neck or shoulder I would see a doctor.