The fears of premature burial were well founded given the state of the 19th Century medical profession as outlined in this article: The Dead Ringer: Medicine, Poe, and the fear of premature burial

There were also two editions of this book, originally published in 1896: Premature burial, and how it may be prevented, with special reference to trance catalepsy, and other forms of suspended animation

This topic continues to fascinate:

Agutter, P. S., et al. (2013). Hysterical paralysis and premature burial: A medieval Persian case, fear and fascination in the west, and modern practice. Journal of Forensic and Legal Medicine, 20(3), 133-135. doi:http://dx.doi.org/10.1016/j.jflm.2012.05.006 (ASU access only)