So far I have two theories regarding how Mr. Bearcy arrived at this new state of consciousness:
1) Mr. Bearcy has been with William for so long, through so many feels, that he has become Real– like all toys that are truly loved (a la the Velveteen Rabbit).
I am hesitant to accept this theory since Mr. Bearcy’s photo (from his Tumblr and Twitter accounts) does not give the appearance of a bear who has become Real. (“By the time you are Real, most of your hair has been loved off, and your eyes drop out and you get loose in the joints and very shabby.”)
2) William Darcy’s tears have magical powers. (Possibly similar to the tears of a phoenix?) Mr. Bearcy has been soaked with those tears (frequently, according to Bearcy’s Twitter), and it seems reasonable that the residue would concentrate daily (when the bear dries out between weep-fests) so perhaps the concentrated residue of William Darcy’s tears reached a critical mass on Friday– sufficient magical power to allowed Mr. Bearcy to become fully self-aware.
Given the possibility that William Darcy’s tears are magical, I think perhaps the staff at Pemberley Digital should be warned about the pool. (According to Darcy’s Diary, the pool is stocked almost entirely by his tears.)