Whew! Scary, then adventurous (as Harry is!), then terrifying and sad and sweet at the end.
I think it says a lot that Snape would be so unnerved by his inner fear made flesh that he's "pale and paralysed" on the floor. (I love the alliteration!) That he can't even trust his voice. How sweet Harry's "sudden, fierce embrace" is, and his saving-people thing that rescues Snape not only from his boggart, but his own self-doubt!