Bet it was from all the different sounds coming in and trying to pick out different voices from everything else during a mission. Ends up as a jumbled mess that makes him freeze and invokes tinnitus, so he's just got a thousand yard stare until Cheavy finds him and drags him to a quiet spot behind a wall. Calms him down before demanding to know what the hell that was about, to which Medic can only whimper out an apology. Perhaps not wanting to tell him about his sensitivity to certain sounds and sensations or what it stems from.