hanabal, there are several scary truths to that about people being buried alive, but most/all happened well before modern times. Mainly, we now embalm before burial, so if you're not dead before embalming, you're dead afterwards
And yeah, quite a few people were buried alive. They have exhumed a rather distressing amount of graves that had clawmarks on the inside where the person tried clawing his/her way out of the casket..
Also, during hte 18th/19th centuries, they would put a pole down with a string and a bell on the top side. The string would extend into the coffin so that if someone were alive, he could pull the string to alert someone above so they can dig him up. There were people who stayed at night to listen for any bells. From this, we get the terms, "Graveyard shift" and "Dead Ringer"