I Cactus fell over and limped in one day?

Hi There, I have a 36 inch cactus (don't know what kind...similar to pictures of Cleistocactus Strausii)...had for about 8 years....growing away fine and dandy....then last week it just limped over at the half way point...totally in half. The only thing I can think of is that I had the window open for 0 minutes while I cleaned the window, and it was about 50 outside...but I can't image that that cool ares for such a short time made my cactus fall over like that? I have lifted it up with an elastic and attached it to the other cactus to hold it up...but is there something else I should be doing? Base seems fine,..there are 2 steams in the pot other is fine...but the droopy one has some areas of thin growth..then thickens, then thin again? Thanks in advance for your time. :-)