Man, if folks don't water it down (even then, it's dangerous over time)..... Basically gonna burn your nasal passageways and other oropharyngeal surfaces. Not sure if burns to the point of bleeding could then get oxygenated enough to cause arterial gas embolism, but it is a risk from ingestion of concentrated H2O2.
Hydrogen peroxide is a caustic. And concentrated exposure can lead to respiratory failure.