Before there were the medications and electronic means we have today, a person in a coma, catalepsy due to s brain disorder, in crisis during a fever, could be easily mistaken for dead. Not every family could afford embalming, which became more common after the Civil War, so a person either had ice around them where possible, or were buried when arrangements could be made. In the interim, a person who was not embalmed could awaken. Poe was subject to catalepsy, and had a dread fear of this happening, which he wrote of in “The Premature Burial”.
That would freak me out. Imagine waking up in a coffin! ACK!