In the movie 28 Days Later (and, to a lesser extent, the graphic novels/TV series The Walking Dead), there is a character who, because of some unfortunate circumstance, found himself in a coma. When he woke, he found that the world was quite different and had no knowledge of the events which happened in the preceding four weeks. To me, this implies that the hero was in the coma for at least three weeks. When he woke, he was clearly well enough to outrun some of the infected for at least a little while.
Is that even possible? Can a coma patient survive several days unattended?