"I take it all back, this is fun," Sherlock said, his voice dripping with the sour tones of sarcasm. The pair had been standing motionless in a winding queue of over-excited visitors for almost twenty minutes now, and even John had to admit that this, in his roommate's words, was tedious.
"OK, Sherlock, I get it. But I promise you, it'll be worth it. Look, they've got stuff for you to look at on the way, see?" John pointed to the black-and-white optical illusions painted on either side of the packed queue line, seeming to swirl and pop out of the walls at the visitors.
"Cheap tricks, easy to ignore once you know how they work. Don't you see, John, it's mind tricks, all mind tricks. That's how rollercoasters work – they get you all hyped up and jittery, anticipating the worst when you get on the ride. You're doing all the work for them – no matter how safe or tame the supposed 'thrill' ride actually is, you'll exit it feeling exhilarated and oblivious to the fact that-"
"Sherlock, shut up! For Chrissake, yes it's all mind tricks, yes it's safe, but that's the point! Getting scared then being safe, it gives you a boost of adrenaline, which is what people crave" by this time, the pair had reached the head of the queue and were being ushered to their seats by an acne-ridden staff member in vibrant dungarees "Just give it a whirl, Sherlock, you might be surprised."
Settling into his harness, John resolved to ignore his flatmate's infuriating indifference; he hadn't ridden a rollercoaster since… well, since before his army days, that was for certain. Decades. Felt like millennia. He was going to enjoy this, regardless. The ride jolted, their cart starting down the track. A toe-curlingly slow ascent; a pause; the curved descent, forcing a yell from the doctor's smiling mouth; corkscrews, loop-the-loops and twists followed and a mere 50 seconds later, the cart jerked to a halt, back at the beginning of the exhilarating ride. John let his head loll back against his seat, a weak chuckle escaping his lips – how he'd missed this! It was all very well getting his adrenaline kicks being pursued by a killer, as happened far too often for his liking, but with this he knew he was safe, so he could enjoy it. Smiling languidly, he turned his head to glance at his friend.
John's mouth fell open as he stared. Sherlock was seated rigidly beside him, tightly secured in his harness, even more secured by his hands, curled into tight fists with white knuckles around the arm-rests on the ride. His curly hair was plastered to his forehead, glistening with sweat, just above the screwed-shut eyes. His chest seemed to be almost convulsing – his breath was ragged, uneven, coming in short bursts.
"Sherlock? Wha- are you OK?" John gabbled.
Unable to reply for the moment, Sherlock merely opened his mouth to gasp, breathing deeply, clearly trying to calm himself. He rested his head against the padded headrest, trying to relax his eyes and shaking.
"I don't… understand it. Never… never before have I… It's the adrenaline... I've... I've been betrayed by my body…"
"Wait…" John desperately tried to stifle an explosive snort of laughter, "the ride did this to you?"
"Of course, John! My symptoms are evidently caused by a rush of adrenaline – something I can't control; I don't believe my body is betraying me like this. How on Earth did you enjoy that?"
Unable to stop himself, John's own chest started convulsing, this time with fits of laughter. He doubled over in stitches, managing to choke out "I told you so! Ha, I told you!" between giggles. "You've just got to relax, trust that there's no real danger, then maybe you won't throw up next time."
"I didn't throw up, there's no need to exaggerate." Sherlock sighed, lifting his head up to meet John's eyes, "How? How do I train myself – my body – to not react like this?"
By this time, all passengers were being invited to exit the ride. When Sherlock's still shaking legs managed to get him outside, John flashed him a grin – this was going to be fun.