Not that it really matters, because he wouldn't have lasted a week without the support equipment, IV fluids, etc. "He was just lucky" is equally stupid. Because the writers didn't bother to explain the magic scenario, the viewers are trying...
Exactly which is why viewers are equally as confused on the passage of time in the prison. Is Rick still going insane after a week - 2 weeks in the prison - how long?
Some of the posters here have suggested it's only been 1 week since Andrea/Michonne got to Woodbury - Lori dies - baby is born - they go get the formula - Rick has faux conversations with folks on phone - Glenn and Maggie are held prisoner - Tyreese and company show up - Daryl gets captured - Merle and Daryl head off into the woods - Rick sees Lori in wedding gown on prison balcony.
Like with Carl's amazing recovery - the passage of time simply doesn't make sense - at least to me.