Originally Posted by
Fish Creek
Usually because the Captain has blacked out at altitude and second in command is dizzy. They will then descend to full oxygen control before landing at remote site. Nothing really to worry about unless you are on the plane.
Or venomous snakes have gotten loose from the cargo hold (I hate when that happens). Or a UFO nearly hits the plane and it (the airliner, not the UFO) has to descent to escape (I think this happens a lot with Allegiant).
There may in fact have ended up being no problem at all, but if the onboard computers detect a problem, they may have diverted to the nearest airport not only where they have facilities but also where they could quickly get clearance to easily land (L.A. area being much busier).