I'd say his fall started when he fucked up bad against Murray at RG after having 5-3, *30-0. From there it's turned into shit for him.
I think that may be when his confidence took a severe hit, but he did make the QF of Washington and he beat Isner in Montreal. He was playing well vs Monfils. Then he choked embarrassingly, got injured vs Fognini in Cincinnati, then lost another tight match vs Falla at the Open. His results and performances, before/after, tell the story.