Oxygen is only needed at the highest altitudes. O2 is only used on 8000 meter accents and many of the elite climbers do not use it anyway.
For most, altitude begins to be an issue above 8K feet but in my experience most folks start to have issues above 10K.

Here in the bay area we have earthquakes and then the potential for civil unrest.
Other than that just the normal pitfalls of everyday life.
I climb, hike, trail run and such; this adds a bit more potential for problems.