I received a pack of Wyeast American Ale yesterday and popped it into the back of my fridge only to find this morning that it may have partially turned slushy from the (evidently) colder area in the back of the fridge. It definitely wasn't frozen solid, but I could hear a slushy mixture inside. I immediately pulled it out and moved it to another area that I know won't be as cold. I would estimate the duration of time in the fridge was about 18-20 hours (but that time would include chilling from ambient temperature.
Have I damaged the yeast beyond repair? Is the only way to determine the effect to smack it prior to brewing to see if it swells properly? Any recommendations on a course of action in either case? Should I go ahead and pitch another pack to be sure or is that overkill?