GREY'S ANATOMY - "Shock to the System" -- After weeks of concealing the fact she was pregnant and miscarried, Meredith at last tells Derek and is finally cleared to return to her surgical duties in the wake of the hospital shooting spree; Cristina experiences post-traumatic stress disorder in the midst of an operation; and Bailey refuses to let Alex operate until he agrees to have the bullet in his chest removed, on "Grey's Anatomy," THURSDAY, SEPTEMBER 30 (9:00-10:01 p.m., ET) on the ABC Television Network. (ABC/ERIC MCCANDLESS) SANDRA OH, KIM RAVER