Yes sudden cardiac death is painful.
When a person dies of cardiac death they will usually experience chest pain, shortness of breath, nausea, vomiting etc.
The arm may also be numb and then within a few minutes or so the person experiencing cardiac arrest will usually lose consciousness.
It's very important to get an ambulance on the way if someone is going into cardiac arrest.
The sooner you get medical attention the higher chance you have at surviving.
Dying of cardiac arrest or a heart attack is usually not sudden and instant but sometimes it can be.
It can happen to anyone at any age.
Yes you can die instantly from a heart attack if the heart attack is severe enough.
Some people who have a heart attack fall down instantly and die instantly from the heart attack and sometimes they fall down and then take a few minutes or so to die from the heart attack especially if they have no medical attention available.
If you think you're having a heart attack call 911 and get an ambulance on the way just to be safe because you might have a small heart attack and feel the chest pain and other symptoms of the heart attack.
Then the heart attack symptoms and feelings may go away and then you might also have another heart attack and die.
So always get checked out and get emergency medical attention for the heart attack.
Most people who experience heart attacks do eventually recover as long as they get the medical attention when needed.