What happened to Ichigo in Urahara's training area after meeting Byakuya (for the first time)?

I understand that during his initial training with Urahara something occurred that gave him (or awoke in him)

but hardly anything is said on the matter. And how come nothing like this never happened before, to the point of Urahara trying to make it possible. For Ichigo just happened?

And how does this play into