Napping, sex, and abstinence.

Isn't it nice to close your eyes and catch a little snooze while flying? You can lean back, relax, and nod off, knowing that the trusty flight crew will take you safely home.

In fact, it's so nice that the flight crew may be snoozing, too.

The latest suspects are the pilots of Northwest Airlines Flight 188, who flew 150 miles past Minneapolis last week while ignoring queries from air traffic controllers and fellow pilots for more than an hour. They claim they were awake. We'll see. But in general, sleep happens. "Pilots on occasion do take controlled naps," an aviation consultant and retired pilot tells Los Angeles Times reporter Hugo Martin.

Martin details several known incidents. In 1998, an entire three-person crew fell asleep while flying a 747 across the Pacific. Six years later, another pilot admitted that he and his first officer had nodded off while flying from Baltimore to Denver. This year, two pilots fell asleep over Hawaii, and one of them admitted to taking regular planned naps while in flight.

Scary, eh? Of course, the Hawaii crew was fired. And thank goodness the FAA bans napping in the cockpit. We can't have pilots snoozing.

But wait a minute. When exactly are these folks supposed to sleep?

A spokesman for Allied Pilots Association says flight crews are falling asleep because airlines, under financial pressure, are pushing them to work as many hours as the law allows. "We have trips now that have five legs a day for several days in a row," he tells Martin. The law requires rest periods between eight-hour flying stints, but pilots say airlines are counting driving time between flights as rest time.

Which brings me to sex.

I know: Not everything is about sex. But bear with me.

When I was in college, I loved studying philosophy. If I were put in charge of a philosophy class for a day, I'd break the students into groups of three and give them the following problem to work out: Which is more important—food, sleep, or sex?