Not any more dangerous than sitting in the same room as another human or animal. You might notice some off-aromas. But then you might notice that from another human or animal (or even yourself). Some fermentations can be downright nasty - "rhino farts" are particularly associated with EdWort's Apfelwein.
Don't pass out and fall to the floor for several days at a time - CO2 is heavier than O2.