In the winter, it's common to see porcupines in the tops of trees in the Rio Grande Bosque. Which raises the question: do they ever fall? In January 2022 I encountered a porcupine for which, apparently, the the answer was yes.
The porcupine was lying on the bare ground, directly below a branch. The porcupine had bled before dying, but I didn't see any specific evidence that it was shot or otherwise attacked. My best guess is that the porcupine fell from the tree and hemorrhaged briefly from its injuries as it died. In hindsight, I should have turned over the porcupine with a stick to examine it for gunshot or attack wounds; their absence would have strengthened my guess that the porcupine had fallen.
As this online article mentions, fatal porcupine falls aren't that rare. When they do fall, they can impale themselves on their own quills. Self-injury from quills is common enough that porcupine quills have evolved to include an antibacterial coating. That coating may reduce the chance of infection from a quill injury, but it won't prevent a porcupine from bleeding to death.