Sleeping together was not something they tried to make a habit of. All of the incidents, or almost all, were unintentional, at least on the conscious level.
The point was, Green did not have any plans of mentioning in casual passing that he'd had a tendency to fall asleep on his rival since childhood, and neither should Red if he knew what was good for him.
Red may or may not have known what was good for him, but this was an issue he agreed on.
They shook on it.
Two children lay wide-eyed on an adult bed, captivated by the movie on TV. One hand reached for another; the gesture may or may not have been mutual, but eventually small hands clasped. As the night went on, covers came up to keep the shivering boys warm. Eyes closed; shoes had long since been kicked off for the sleepover. The TV movie played on.
In the morning, both children would be found to have a high fever, and their families would take them separately to the doctor and berate themselves for not noticing sooner.
Years later, both boys would flush and glare at parental mention of how cute they'd looked, and being delirious at the time would turn out to make a very good excuse.
Despite being the "Pokemon Professor", Green's grandfather didn't often have the actual creatures on hand, and never ones that were suitable for children to play with. Green pretended not to be disappointed, and he and Red spent plenty of time observing the wild Pidgeys and Rattatas from a distance, but neither hid their enthusiasm when the couple next door were asked to take care of a relative's pet Arcanine.
Their neighbors were kind and considerate when the excited pair showed up at their doorstep, and as the Pokemon was fully domesticated, with permission from Red's mother the two were allowed to play with it. The Arcanine was like a large, friendly bear, nothing like the fighters seen on TV tournaments, but the two boys happily chased it around the yard until the worn-out Pokemon settled down to nap.
Red and Green continued trying to play with the creature, unperturbed by its lack of consciousness, but a half hour later saw them cuddled up along with it, contentedly snuggling into the soft fur. They were fast asleep when Green's sister came to pick them up, and the photo snapped of the three in their sleeping state was never discovered by either of the boys.
The night before the boys' long-awaited Pokemon journey, sleep looked unlikely. The Professor had refused to give any fuel for their already giddy excitement, sending Green to bed instead - a plan that had failed abysmally. Twenty minutes later Green had snuck out of the house and invited himself into Red's room; now, armed with all the magazines they could find, the boys were feverishly guessing at which Pokemon they might receive.
Some were easily ruled out as being common and uninteresting. Others, such as Ponyta and Gastly, were too big or too dangerous. Neither of them wanted a Normal-type or Fighting-type, or anything that didn't have flashy yet practical attacks, and there was no chance even Green's grandfather could hand over something like a Dratini.
They barely made it to midnight before closing the picked-at magazines and, after promising not to fall asleep yet, doing exactly that. At some point, their shoes were removed and loose limbs lifted onto Red's bed; by morning, Green was scrambling back home to get fresh clothes and still beat Red to the lab.
The magazine clippings were left for Red's mother to clean up.
The most embarrassing situation of Green's life, as far as he was concerned, had never happened. And if it had, it was all Red's fault.
It was a complete fluke that Green had fallen off his Gyarados while Surfing, naturally, and it was just bad luck that Red happened to be around. As he would point out later, no one had told the other trainer to dive into the water after him. If Green hadn't had to think about his rival's safety in addition to his own, he could have been right back on his Pokemon and swimming safely away.
As it was, Green had panicked, and both may have been strong swimmers but not as strong as the currents near Seafoam Island. Holding tight to Red, who had gone right for him, Green was able to help keep them above the waves until the currents knocked them straight into foot-deep water by the shore. Exhausted, the two managed their way onto the sand and fell unconscious as the tides lapped at them.
Some time later, Green awoke to wet clothes on one side and a warm, dry sun on the other. His hands had loosened on Red's shoulders (and vice versa) as they slept.
Green made to nudge Red awake, then froze. He was suddenly acutely aware of their closeness, not to mention a sleeping rival breathing softly against his mouth. None of it was on purpose, of course, and all of it was completely the other trainer's fault, but that didn't change the fact that their current position was irrefutably awkward. Green exhaled carefully, wondering if he could just push Red off him before he woke up.
Closing his eyes finally and feeling the low tide soaking his clothing, Green decided that more sleep might do him some good. Red could deal with the awkwardness himself when he woke up.
Green had probably meant to hit Red when he reached the summit of Mt. Silver. Also a possibility was yelling or other physical violence. Red wouldn't really have been surprised at all three.
Any of those, however, depended on Green not slipping during a tussle with some wild Pokemon and slipping partway down the mountain to where Red had found him, alerted by the cries of a frantic Eevee.
Red didn't even try to carry Green all the way up the mountain, even though Snorlax or Charizard could probably have done it. He carried a blanket in his bag, and so instead the Kanto Champion dragged his childhood friend into a familiar cave nearby where the temperature was a little higher and the Pokemon would be less likely to see them.
Inside, Red leaned Green against the wall and eased his snow-soaked jacket off, glad to note that the clothes underneath were mostly dry. Making sure no Pokemon were following them first, Red draped the blanket over his rival carefully and kept watch for the majority of the next hour, both over the boy sleeping inside and the snow falling outside.
The hour passed, and Red yawned. Green was warmer than before, though shivering occasionally, and the snow kept the cave partially hidden. Safety, for now, was not an issue.
Green would be fine, wake up soon enough, and hopefully go back down the way he'd come up the mountain. Red would have no problem staying alert until then.
Green shivered again, more noticeably, and Red decided body heat couldn't hurt either of them.
Slipping under the blanket to sit uncomfortably against the wall, Red leaned Green against him, looking down at his rival. Even in sleep and relaxed, Green didn't seem quite at peace.
Red adjusted the blanket and stared out at the snow. He'd deal with seeing his rival again when he woke up. For now, he'd indulge in a comfortably familiar-feeling nap.
As for Green... Green could decide whether or not to punch him when they were both awake.
And as always, they'd never speak of this again.