Bottling up our fears and frustrations can lead to a malady I call Traveler's Paranoia. Symptoms include a morbid fascination with airline timetables and uncontrollable fantasies of being stranded in the middle of Mexico City without your traveler's checks. Use cabs late at night rather than walking. Unfortunately, men often assume that women on lonely streets and deserted beaches are searching for companionship. Carry a key chain whistle and, if you're bothered by someone, give your whistle a mighty blast.
Mexican cops use whistles to signal each other and to scare off troublemakers.
Until you feel comfortable in Mexico, don't be embarrassed to pamper yourself a little. Travelers on a tight budget should be especially careful not to subject themselves to more of Mexico than they can comfortably handle. When your sense of humor about the situation has worn as thin as the sheets, it's time for a temporary upgrade in accommodations, at least until you get your feet back on the ground.