and suddenly he was rushing forward , sliding into blackness , seeing the dirt walls disappear into darkness before him , and then the walls became narrower-much narrower-terrifyingly narrow-and he was lost in the pain of a squeezing compression that became steadily worse and worse , that crushed the air out of his lungs , and he was only dimly aware that the tunnel tilted slightly upward , along the path , shifting his body , leaving him gasping and seeing spots before his eyes , and the pain was extreme .