Wouldn't being buried alive suffocate a person quickly?

So its been portrayed as a trully gruesome way to go, as a possible explanation for the myth of vampires, etc, etc. But essentially being buried alive means you get tossed in a really small box, and all sources of air get sealed off.
Doesn’t that mean that a person would suffocate really quickly? If someone is unconscious when buried, wouldn’t they basically never really wake up?
In other words, how come its portrayed as a lingering way to die when it seems to me that (as unpleasant as the thought of it is) odds are death would be relatively quick and painless.
Or am I TOTALLY misinformed?

Dunno how quick it’d actually be in a regular sized coffin, depending on circumstances. Houdini demonstrated that he could stay alive in one with no trickery (just staying calm and quiet and breathing normally) for a much longer time than you’d think. Hours? I can look up the cite if you like, got a couple of Houdini biographies around here someplace.

Now if you were sealed into a box knowing that it was a method of execution I imagine time would pass much more quickly and less pleasantly. It’s dark, there’s barely any room to move, you are suffocating and you know that there’s nothing you can do about it. I bet that panic would set in and oxygen would get used up much faster (struggling, screaming, breathing too fast); once the O2 content drops too much and CO2 levels rise you’d start suffocating which would probably suck.

Possibly relevant:

http://www.snopes.com/horrors/gruesome/buried.htm

Mythbustersdid it.