What if Sherlock had taken just a little bit longer to get John out of the fire and he had suffocated in the smoke. Sherlock gets him out but he’s not breathing, so he starts trying to resuscitate him. John regains consciousness, but in his delirious state he turns the mouth to mouth resuscitation into a deep kiss. Sherlock is shocked, but so relieved he just holds Johns face and smiles into the kiss. Nobody realizes what’s happening though. This moment, though John might not remember it once he recovers, is private and just between the two of them and Sherlock will never forget it for as long as he lives.