I think I've realized tonight why I've been told to chill bottles for 3-4 days to let the co2 absorb back into the beer. I just got home from vacation and during unpacking, threw 5 bottles into the fridge and one in the freezer. When I opened the freezer bottle there was a small pfft which had me worried. Then I poured it into a glass. No head. Not even signs of carbonation. I took a sip and it was nice and cold but completely flat. Tell me this is because of too short a chill time and not a problem with carbonation. The first 6er was wonderful but were chilled much longer.