The boy was feeling like trash again. His body couldn't be more destroyed than that... Well, actually it could, but have both right leg and arm useless made him felt like he was at the deepest bottom. He couldn't walk nor had the strength to grab on something to support himself.
Since Dean entered that tunnel that would lead further into the cave, he continued running clumsily until he lost all strength he had remaining. At some point, the tunnel became even wider and inclined, which caused him to trip and roll until the end of it.
That's how he ended up lying on the ground in a lower level of the cave.
Also, he wasn't just hurt but scared as a little cat.
'The "Chaos" here... It's an otherworldly thing! According to what I can see in the environment, there aren't too many Dreads near me, but the few ones that are lurking around are very strong. I am not sure if I am a match for them or not... I even feel some of the 5th generation... That's dangerous.'