Thrilled me—filled me with fantastic terrors never felt before; (line 14)
The possibility of madness creeps into this poem slowly. Here perhaps the speaker seems like he might just be having a weird night. We might say that he's perhaps a little hypersensitive, a little more imaginative than is really good for him. But remember, all it takes to thrill him and terrify him is the "rustling of each purple curtain." Kind of a strange thing to set you off. We can feel him teetering on the edge already.
Back into the chamber turning, all my soul within me burning, (line 31)
Now the panic starts to build. Before he was just thinking some scary thoughts; now he feels like his soul is on fire. Again, nothing has really happened yet, just a mysterious knock and the empty darkness outside. Someone in a better mental state might just head back and take a nap. This guy, though, is already pretty unbalanced by his grief and his weird night. Just think how much worse it will get once he meets the talking bird.
To the fowl whose fiery eyes now burned into my bosom's core; (line 74)
More burning here, and again, it's hard for an outside observer to see exactly why our protagonist is so upset. Have you ever looked at a raven's eyes? They can be a little intense in a beady, birdlike kind of way. We'll even give you spooky, if you like. But fiery? We just don't see it. Of course, this is clearly an unusual bird, and it might have unusual eyes. Still, we feel like our speaker's already fractured mind makes him more likely to be really bothered by this bird.