The first time it happens, he's in the bullpen.
Derek is the first to notice. He'd been able to tell something was off from the moment Reid arrived half an hour late, already looking agitated and unbalanced.
From his position at the coffee machine, he notices the young genius chewing the end of his pen, a habit he knows Reid hates in other people. Watching more closely, he notices Reid curling into himself slightly when the two people sat at the desks either side of him – desk agents, neither of them part of their team – start a heated conversation about last night's soccer. He watches Reid reach up to cup his left hand over his left ear, fingertips massaging his temple almost subconsciously as he continues trying to focus on his work.
"Spencer," Derek calls, making his way over to Reid's desk to check on him, "everything okay?"
Spencer doesn't seem to even register Derek's voice, eyebrows knitted as he stares at his case file.
"Hey, Spencer?" Derek repeats, standing next to his chair, "pretty boy?"
Reid finally looks up, and Derek doesn't miss the way he squints up at him, like the lights are hurting his eyes. "Hm?"
"Is everything alright?" Derek repeats, concern lining his features. "You seem a little stressed over here."
"Oh," Reid mumbles, swallowing awkwardly like he's trying to find some words to say, "I- uh. I'm fine. S'loud in here."
Derek raises his eyebrows at that. Sure, there's the chatter of desk agents and the general sounds that come with being in a community workplace, but he wouldn't have said it was particularly loud.
"Do you wanna take a coffee break with me?" Derek asks, holding out his steaming cup.
"Oh, no, that won't be necessary," Reid rushes to decline his offer, eyes flicking over Derek's shoulder before landing back on him.
"Well, if you change your mind, just come get me." And with that, Derek returns to his own desk.
His desk faces away from Reid's, his back angled towards the younger agent. He works on updating case files for a half hour and almost forgets about Reid's strange behaviour. Distantly, he registers a muted but persistent high-pitched humming coming from somewhere behind him. It takes him a few moments to realise that it's not a malfunctioning computer or faulty light, but a person – Reid. He swizzles his chair around and spots the young genius curled up in his seat, eyes squeezed shut, hands cupped over his ears but not pressing down.
Derek is on his feet in an instant, crossing the small distance quickly. Nobody else seems to have noticed Reid struggling – he's not surprised, really, because nobody else in the bullpen besides the two of them are part of the BAU team. Hotch and Gideon both sit in their offices above the ground space, oblivious.
"Pretty boy, what's going on?" Derek asks quietly, crouching down in front of the genius' chair.
Spencer whines in response, turning his head away from Derek's voice like it hurts to listen to. Derek's eyebrows knit together in concern, confusion pushing through.
Derek is about to repeat the question when two agents burst through the bullpen doors, one following behind the other. They're in the middle of a heated argument, they're shouting, and it pushes Reid over the edge.
Reid's right palm clamps firmly over his right ear, pressing down painfully hard. His left forearm flies to his mouth and he bites down hard, a strangled noise escaping from his throat. His eyes stay squeezed shut as he hunches over completely, his nose nearly touching his knees.
Derek is immediately at a loss for what to do. He briefly wonders if he should pull Reid's arm from his mouth, because that has to be hurting, but he knows how Spencer is with touch and he doesn't want to add it to the list of things Spencer is dealing with right at this moment.
"Hotch!" he calls in the direction of Hotch's office, and then towards Gideon's. Reid forces out an even more pained sounding whine at the loud noise. "Hotch, Gideon! Get down here!"
He sees both the senior agents lift their heads at his calls, both wearing equally concerned expressions, and then they stand up in unison, emerging from their offices. People are staring, but Derek doesn't notice, eyes fixed worriedly on Reid.
Hotch takes one look at Reid and jumps into action.
"Everybody out," he commands sternly, loudly. "Outside, now."
The desk agents immediately stand to leave, filing out of the main doors quickly and quietly, leaving the bullpen empty apart from the four.
"Spencer, hey," Gideon says gently, kneeling in front of Reid's chair. "Listen to me. You're okay. It's okay."
Reid replies with a garbled moan that tears at Derek's heart, and then a second cry that practically screams make it stop. He's drawing blood from his arm now, and Derek winces, looking away.
"I know. It's okay, it'll pass," Gideon coaches gently, "you're safe. It's just Morgan, Hotch and us. It's okay."
Hotch approaches them, and Derek notices he's shut all the windows, blocking out the sounds of traffic coming in from outside. Hotch stands behind Reid's chair and reaches down to firmly place his own palms over Reid's ears, his right hand covering Reid's.
Reid struggles against the touch for a few moments, twisting and turning uncomfortably before his body falls into a rocking motion, his torso moving back and forth quickly.
"Shouldn't we move his arm?" Derek asks, his voice tight. "He's hurting himself."
"He'll stop when he's ready," Gideon replies evenly. "If we restrain him, he won't calm down."
To Derek, it doesn't look like Reid is ever going to be ready to stop. But, after five tense minutes of rocking and whimpering and biting, Reid's movements slow down to an eventual stop, his torso stilling and his arm falling from his mouth, wet and bruised and bleeding slightly.
They let him sit in silence for a few more minutes, Hotch's hands still covering Reid's ears, the younger agent's eyes cast down as his head droops against his chest, exhausted. After a moment, Gideon slowly puts a still hand into Reid's line of vision, holding it there until Reid hesitantly looks up, his eyes focusing somewhere above Gideon's left eyebrow.
"Ready?" Gideon asks, though it's so quiet Morgan thinks Gideon must know Reid can't hear it. Reid must make some sort of signal that Morgan misses – or maybe the lack of objection is enough – because Gideon nods at Hotch, who gently takes his hands away from Reid's head.
Reid seems to deflate, his chin dropping back against his chest tiredly. For a few moments, there is absolute silence across the bullpen, save for the sound of Reid's slowly evening heavy breathing. Morgan almost isn't sure if Reid's fallen asleep or not, until Reid finally looks up, squinting down at Gideon in the light.
"Better?" Gideon asks, and Reid nods, averting his eyes.
"I'll get the first aid kit," Hotch announces quietly. Morgan stands back, feeling helpless and confused in equal measures as Hotch disappears into his office and returns back with a green plastic box.
Hotch crouches down next to Gideon, opening the box on the floor and pulling out some antiseptic wipes and a bandage. Reid wordlessly offers his arm to Hotch, the first lucid move he's made since the meltdown.
"This might hurt," Gideon warns as Hotch tears open one of the wipes. As soon as it makes contact with Reid's broken skin, Reid lets out a high pitched squeak, his unoccupied right hand flapping frantically at shoulder height.
"Almost done, Reid," Hotch reassures in a voice Derek silently knows is usually reserved for comforting Jack. He wraps a stark white bandage around the wound and tapes it off with a wide skin-coloured bandaid.
Reid takes his arm back, letting it drop down against his thighs. After a moment, his right hand forms a fist against his chest and he moves it in two clockwise circles.
"You don't need to be sorry," Hotch states, and Morgan realises it must have been sign language. He absently wonders if Hotch or Gideon or both are fluent, or if they just know as much as Reid has told them.
Reid shakes his head, bringing his right fingertips to touch his lips before moving his hand away from his mouth until it ends palm down a small distance in front of his chest.
"You're not bad," Gideon says with a tone that radiates don't be silly. "You can't help getting overwhelmed. You dealt with it until you couldn't anymore. We understand."
Reid doesn't make any more attempts to sign again after that. The four remain in silence, Gideon kneeling, Hotch crouching, Morgan stood off to the side, arms crossed over his chest. After a minute, Hotch pushes himself to standing, turning towards Morgan.
"Morgan, could you find the other agents and tell them to come back to work in five minutes? Meet me in my office when you're done."
Morgan nods, grateful to have something to do with himself after standing helplessly at the side for the duration of the events. It takes a while for him to find the other agents. They're sitting in the bureau cafeteria, and Morgan passes on Hotch's message before turning around and taking the elevator back up to the right floor.
When he re-enters the bullpen, the other three agents have gone. He knows Reid is probably with Gideon in his office. He makes his way up the steps onto the balcony and knocks on Hotch's office door, waiting for the 'come in' before he opens it.
"Morgan, sit down," Hotch gestures towards the seat in front of his desk. Morgan does so, slightly awkwardly.
Hotch waits for Morgan to speak first. Morgan waits for some sort of explanation, but when none comes, he rubs his palms against his trousers and sighs. "Hotch, what the hell was that?"
"What you just witnessed was an autistic meltdown," Hotch says simply.
"He's autistic?" Morgan raises his eyebrows. "I know we all suspected, but… I didn't think he'd actually been diagnosed."
"Gideon and I knew before he joined the BAU," Hotch confirms, "which is why we knew what to do."
"Have you seen this happen before?" Morgan asks.
"Not personally, no. But I know Jason has. Reid asked him to tell me what to expect and what to do should something like this occur."
Morgan swipes a hand across his face, processing the new information. Everything suddenly makes sense, from the way he's seen Reid act on cases to the way he'd been behaving all morning.
"He's not comfortable with the others knowing," Hotch informs him, a note of warning in his voice.
"I get that," Morgan says truthfully. "They're gonna find out sometime, though. What if something like this happens in the field?"
"Then we deal with it when it happens," Hotch says simply. "Reid has proven himself time and time again to be a valuable member of our team. If we have to make accommodations for him in the field then that's what we'll do."
Morgan nods. Through the window, he sees the other agents begin to file in. His eyes fall on Reid's desk, unoccupied, and all he knows now is that he will do anything he can to protect his little brother.
Next door, he hears Gideon's warm laugh, and thinks Reid might just be getting back to himself again.
It's enough for him.