The second time it happened was after Sherlock fell into the Thames.
John had gotten home from a late shift at the hospital and was watching Bond films on the telly when Sherlock burst in the door, sopping wet.
"What the bloody hell happened to you?"
"Apprehending a suspect. Fell into the river." Sherlock scowled. "I lost him." He stumbled over to the sofa and sat down with a squish.
He tugged his phone out of his pocket and growled as he threw it at John, who deftly caught it. "Completely ruined! I'll have to ask Mycroft for another one. Damn."
John blinked at him, holding Sherlock's waterlogged mobile phone, and wondering just when he'd lost his mind. The day he'd agreed to move in with a lunatic, John supposed.
"You're getting the sofa wet," John noted mildly.
Sherlock just stared at him.
"You might want to change. And take a shower."
"Why?"
"Because you're soaked?" John got up and knelt at Sherlock's feet.
Sherlock was starting to shiver, and his eyes looked slightly dilated. He was tensing up a bit, but not from any obvious injury. "Let me make sure you weren't injured." John reached over to grasp Sherlock's wrist to check his vitals, and wasn't terribly surprised to feel how cold Sherlock was. "Right, get up, we're going to get you out of these clothes."
"I thought you'd never ask, John," Sherlock joked. Or at least, John hoped he was joking.
John just rolled his eyes and steered Sherlock to his bedroom. He sat Sherlock down on the bed and started stripping off his wet clothing, Sherlock not saying much or offering up any form of protest.
Once Sherlock was down to his pants, John grabbed a towel from the bathroom and dried him off.
"You want to change those yourself?" John gestured.
Sherlock just pulled off his pants in front of John and tossed them on the floor.
"Okay. Not really what I meant, but that's fine." John studiously turned his gaze elsewhere and handed Sherlock the towel, but Sherlock just sat there holding it. "Oh, for fuck's sake!" John grabbed the towel and rubbed Sherlock dry. Did he have to do everything?
When he pulled back, he noticed that Sherlock was refusing to make eye contact. "If you didn't want me to touch you there, you should have dried it yourself!" John sighed with exasperation as Sherlock just sat there. Well, hypothermia did tend to cause confusion. "Time for bed."
This time, Sherlock did look at John, panic written over his features. "No whinging, now. Put these on–" he tossed Sherlock his pyjamas– "and I'll go see if we have any spare blankets."
John rolled his eyes as he collected the quilt from his bed upstairs. Honestly, for being so arrogant, Sherlock had chosen some strange things to be modest about. After all, John was a doctor. There wasn't much he hadn't seen before. In fact, he'd seen Sherlock naked a few times already. Sherlock had a tendency to pop out of the shower straight to the kitchen when he realized he'd forgotten to set a timer for one of his experiments. The first time, there was still soap in Sherlock's hair, and John had just stood in the kitchen staring stupidly, holding the tea kettle in his left hand.
When John got back to Sherlock's room with his small pile of blankets, Sherlock had managed to get his bottoms on but was still struggling with the shirt.
"Here, let me help you." John gently pulled the shirt over Sherlock's head, guiding his arms into their proper sleeves. He tucked Sherlock under the covers and piled the blankets on top. "Let me get your temperature right quick."
"John..." Sherlock croaked.
"What is it?"
"Will you–" he frowned, but he seemed to struggle with the words, gesticulating weakly with his hands.
"Let me get the thermometer first. Okay?" John grabbed the instrument from the bathroom medicine cabinet, quickly sterilized it, and ran back to Sherlock's room. He shoved it under Sherlock's tongue. "Don't move until it beeps."
Sherlock's shivering was worse now, John noted, even though he had changed into dry clothes.
The thermometer beeped. 33 degrees. John swore. Definitely in the danger range.
"All right, shove over." John shucked off his shoes and socks and pulled back the covers, crawling in next to Sherlock. "This will help you get warm. So no complaints."
He forced Sherlock onto his side, facing away from him, and snuggled up to flatten his chest against Sherlock's back. Even though he was only doing this to raise Sherlock's temperature, and Sherlock was shockingly cold, the physical contact was... nice. He'd missed this. Although he hadn't done it with a man before. Or someone taller than him, he noted grumpily. Sherlock didn't say anything, or try to move away, but John could feel the tension in his back and shoulders.
"Relax," John whispered.
Eventually, Sherlock stopped shivering and his breathing slowed. John let himself drift off as well.
When John awoke, Sherlock was still asleep. The hand at his wrist was warm now, and Sherlock's skin was a healthy colour, so John deemed it safe to extricate himself.
John made himself a cup of tea before retiring to his own bed, and when he woke up it was to the gentle strains of Sherlock's violin. Sherlock didn't mention the prior night's events (not so much as a "thank you" for not letting him freeze to death), and neither did John.