Sherlock had slipped in and out of sleep during the night. It wasn't nightmares that kept him up as much as it was just his really weird circadian rhythms.

When the first light started filtering in through the curtains over the windows in his bedroom, he heard and felt John start to stir. He could tell he needed to get up but he didn't want to at the moment. So he stayed still, keeping his breathing even, his eyes closed, his sense on alert.