It was overwhelming, how much he had screwed this up. He should have just let it go. It wouldn't be the first time his feelings went unreturned and it certainly wouldn't be the last. Even if Elena's not angry that's... not the point. They had something good, a really good- great even- friendship and he had ruined it. She would know now that he had some sort of feelings for her and wouldn't want to hang out with him anymore. Not to mention if Damon ever found out.
For a moment, the panic attack became even worse, the teen gasping for breath and having to bend over, hands braced against his knees as he fought for breath. "Oh god, he's going to kill me. He's going to rip my throat with out his sharp fang-y teeth," Stiles breathed out shakily. Little by little, his breath was coming back, calming down as the attack slowly passed. Glancing up at Elena for the first time since the attack happened guilt rolled in his stomach at the sight of her tears. He did that. He'd made Elena cry.