I think this might be corrupted advice of not lying down to see if the problem goes away before calling 911. Lying down and waiting instead of getting help is certainly worse than calling 911 and then lying down.
If you think you are having a heart attack, call the emergency services.
They’ll run through a few questions and advise you whether or not to take aspirin.
Like all drugs, there are some people who should NOT take aspirin- even if they are having a heart attack. The EMTs and the Emergency operator will try to determine whether you are one of those people or not before giving you aspirin or advising you to take it.
Just to play devil’s advocate, just as some people with heart attacks think they have heart burn, some people with bleeding stomach ulcers think they’re having a heart attack- and they REALLY don’t need aspirin.
you should call 911 first, then take the aspirin. The reason you may want to lie down is because if you have had an infarct some of the heart muscle will be damaged and probably your heart won’t pump at 100% as it used to, this is perhaps heart failure and in heart failure your heart will pump more efficiently if you sit rather than lie down. Also your blood may back into the lungs from your heart during heart failure, and this feeling of drowning in your own fluids can be relieved by sitting up.