Why your airplane dives after losing cabin pressure

Information in an article at Salon will allow you to remain a little more calm if/when the plane you are flying in starts to nosedive after a loss of cabin pressure:

The American Airlines incident over Miami was, at worst, a rapid decompression.

The first thing pilots do in such a scenario is pretty straightforward: They don their cockpit oxygen masks and commence a rapid descent to an altitude no higher than 10,000 feet. Even with a total pressure loss there are several minutes of supplemental oxygen available for both passengers and crew, but the protocol is always to get down as quickly as possible. When the passenger above spoke of "descending really fast," this isn't because the plane was crashing, it was because the crew was doing what it was trained to do. I'm sure it was startling, but a high-speed emergency descent is well within the capabilities of any aircraft and not, by itself, unsafe...

If, at some point during all of this, cabin pressure falls below a certain threshold -- usually the equivalent of 10,000 feet -- the passenger masks will deploy from the ceiling, exposing everybody to the so-called rubber jungle. This is typically the point where people begin shrieking and picturing their loved ones, but try to relax. The masks are there to assist you; the plane will be at a safe breathing altitude in just a few minutes. And 10,000 feet, the deployment trigger height, isn't very high; in most depressurization incidents you could ignore the masks entirely with no ill effects...