Put incredibly simply, he's going insane.
At first, he's just starting to lose it. He's managed to hold it together thus far, but his "glued-on sheet of self control" can't last forever. He fights it as hard as he can, but his willpower is being depleted quickly.
At 1:29 (Heartbeats hammering at the sight), things get heavier. Things he didn't want to feel, things he was afraid of, surface completely. He stares at his own likeness in his shadow, like he's terrified by his own self.
Then, at 2:15, things change up again. The drums get all crazy, and our friend has just completely lost his mind. He's trapped in his own mind, unable to even communicate with the rest of the world around him. It's like he only exists in the shadow he sees, which is now taunting him with its silence.
Put incredibly simply, he's going insane. At first, he's just starting to lose it. He's managed to hold it together thus far, but his "glued-on sheet of self control" can't last forever. He fights it as hard as he can, but his willpower is being depleted quickly. At 1:29 (Heartbeats hammering at the sight), things get heavier. Things he didn't want to feel, things he was afraid of, surface completely. He stares at his own likeness in his shadow, like he's terrified by his own self. Then, at 2:15, things change up again. The drums get all crazy, and our friend has just completely lost his mind. He's trapped in his own mind, unable to even communicate with the rest of the world around him. It's like he only exists in the shadow he sees, which is now taunting him with its silence.