I have so many other stories I should be working on right now, but I realised, there is simply not enough Big Bang Theory fanfiction with just Leonard and Sheldon being friends. Upon realising that, this plot bunny attacked me, and insisted on being written, so here it is, for your enjoyment.

"Sheldon, you've got to eat something," Leonard exasperatedly told his best friend and flatmate.

Sheldon turned to give the shorter man a condescending look. "Leonard, I am currently working out a groundbreaking contribution to science, the likes of which your lesser brain can barely comprehend. I cannot be distracted by something as petty as food."

Leonard threw his hands in the air, frustrated at his friend's refusal to listen to reason. "You know what? Fine. I'm going to bed. You keep working on your 'groundbreaking contribution to science'."

Sheldon ignored him, already lost again in the mysteries of the universe.

"I'm worried about Sheldon," Leonard confided in his friends a few days later.

Howard snorted. "We're always worried about Sheldon."

Raj nodded. "Yeah, like worrying about what crazy thing he's going to do next."

"No, this time I'm really worried about him," Leonard continued, ignoring his friends. "He's been working on this project for the last four days, and hasn't slept or eaten at all in that time. He didn't even come in for work today, just kept working on his blackboard."

"He's Sheldon," Howard said, shrugging sympathetically. "He'll figure it out soon, and everything will be fine."

"Yeah, I guess." His worries lightening after his friends' advice, he continued eating his lunch while the conversation changed to the female visiting professor across the room.

"Hey Sheldon, I'm back," Leonard said, shuffling through his mail as he opened the door. Looking up, the mail dropped from his suddenly lax fingers.

Sheldon was lying collapsed on the floor beside his whiteboard, looking like a puppet whose strings had been cut. "Sheldon!" Leonard cried, rushing to his friend. He knelt down beside him and shook his shoulder. "Sheldon? Sheldon, wake up."

Sheldon didn't respond.

"C'mon, buddy, wake up," Leonard continued, his worry increasing. "Sheldon, you need to wake up now. Wake up!"

Sheldon's eyes remained closed for a moment more, then his eyelids fluttered. "Leonard?" he asked, his eyes still shut, his voice sleepy. "What're you doin' in my room? You aren't allowed in my room."

"This isn't your room, Sheldon."

"It's not?" Sheldon's eyes finally opened, and he started to sit up. "Why did I fall asleep in our living room?" he asked, turning to look at Leonard.

"Probably because you haven't slept in four days, Sheldon," Leonard said, his voice tinted with frustration.

"I had an epiphany, Leonard, I couldn't waste time sleeping!" Sheldon said, his voice regaining a hint of its normal arrogance. He got to his feet, then swayed as his face turned white.

Leonard quickly got up and grabbed Sheldon's arm to stop him from falling back to the floor. "See, this is what happens when you don't sleep or eat for four days," Leonard said with a hint of smugness.

"Maybe you're right." Sheldon rubbed his eyes with the arm Leonard wasn't holding on to, looking for all the world like a sleepy little boy.

"You're admitting I'm right?" Leonard asked, with more than a hint of disbelief. "You must be more tired than I thought! Come on Sheldon, time for good little scientists to go to bed." He guided the taller man through the apartment and into his room.

Tucking Sheldon in, he was about to leave when Sheldon reached out and grabbed his arm. "Wait!"

Leonard sat down on the side of the bed. "What is it, Sheldon?" he asked. After the fright from earlier, he really wanted to just get Sheldon to sleep and then relax for a while before the others arrived.

Sheldon tucked his arm back under the covers, then looked up at him with innocent blue eyes. "Thank you, Leonard."

"You're welcome," Leonard said with some surprise. As Sheldon's eyes slipped shut, Leonard got up and walked back out to the living room. Sheldon was like a little brother, he thought. He was often pesky and annoying, and some days Leonard just wanted to strangle him, but whatever came, Leonard would still look out for him.