Great characterization here: Lestrade climbing through the rubble even though it's dangerous; Sherlock's insistence on John, though he can't make clear at first why he's worried about John; Donovan's thinly veiled concern (and happiness that John has been found); Mycroft being difficult because he can't be bothered with the social niceties at this point.

I've had a head injury. I still remember asking questions that I knew I'd asked before because I couldn't for the life of me remember the answers. It's terrifying. For Sherlock, who is even less used to lacking full information or not remembering what he needs, it must seem catastrophic.