Paging Dr. Alex Karev! Grey's Anatomy star Justin Chambers checked himself into the psych ward at UCLA Medical Center -- the same place where Britney is now being treated for bipolar disorder. Justin was "exhausted and suffers from a sleeping disorder," his rep tells TMZ. "He went in voluntarily to get some help." But alas, he and Britney only overlapped for a few hours -- after checking in on Monday, he checked out yesterday.

Yeah, don't count on Britney having the same speedy recovery…