He's been scared before. It's not like he believes that because he's a werewolf he's invincible. He's never been that way. He's smart- he thinks with his brain, not his muscles.
He's never quite worried about the little things that terrify most people. He's not afraid of the monsters in the dark (mostly because he is one); not afraid of spiders (mind you, the huge poisonous ones were creepy, but how many of those were walking around Buffalo?) He isn't afraid of death or snakes or heights or taking risks or making decisions or saying what he thinks.
No, what Derek is most afraid of is himself.
How many times has he relived that moment in his brain, how many times has he seen that boy slam into the wall? How many times has he pictured that wolf, throwing itself at the bars, trying to get to him? He's terrified, not only of what he can do when he means to (although he never means to cause so much damage), but what he can do when he doesn't mean to. And now, with the knowledge that he had been tampered with, who knew what he could do?
Yeah, Derek is pretty afraid of himself. But there's something, or rather, someone, that scares him just as much, if not more.
Derek's pretty damn afraid of Chloe, too.
Not in the usual way. He doesn't run screaming from her when he sees her, doesn't cower behind people when she speaks. But he's terrified of something happening to her. And he's terrified of how she makes him feel.
He doesn't trust. The only people he trusts are Simon and his father, but he knows he would tell Chloe anything. He's already told Chloe things he had never intended to, but his tongue just unravels around her. He just wants her to understand- although understand what, he's not quite sure.
But it's more than that. It's this strange, fierce protection he has for her. It's more then just his inner wolf fighting to protect her- it's his inner man, too. And it's just like that time with Simon but he knows that if anybody ever hurt Chloe they would be faceless to him, and he doesn't even know if she could stop him now.
And these feelings are so scary because they're so new. He's been dealing with this fear of himself for years now- but this new feeling of ferocious protectiveness he feels for her is completely new and he doesn't know how to handle it. He wishes he could ask someone for advice but the only one he can think of is Chloe and he's afraid of talking to anyone about these feelings, let alone her.
(There's that word again, afraid, and he wonders how such a small girl could ever evoke such feelings of fear in him.)