Theo heard Greg's shout and he tried to get up too fast, smacking his head on the bed slats because he was hiding underneath there; by the time he'd crawled out and made it to the room where Greg and Zach were he was covered in dust and had a slight bump on his head from smacking it into the slats.
He came in gingerly, coming up to Greg cautiously like a nervous cat, standing and watching the pair from a slight distance, not confident enough to disturb anyone in the middle of a conversation, his mind caught in a limbo and a memory somewhere.