So everybody knows how much it sucks when you have to pull an all-nighter. But just take a nap during the day, and then get a couple days' worth of good sleep, and you'll be back on track, right? Er, no. According to ER doctor Andrew Herring, "A single night shift has cognitive effects going out for a week." And it's not just doctors (and their patients) who are suffering. Industrial accidents occur disproportionately before dawn as well. But perhaps most surprisingly, it's not just about cognitive ability. Workers assigned to the night shift are at a higher risk for obesity, diabetes, and even cancer.

One study on a group of particularly beleaguered laboratory mice highlighted exactly how crucial a reliable sleep schedule is to our health. Over the course of eight weeks, the lights in the room were dimmed and raised in sync with dawn and dusk for six days a week — but on the seventh, they were turned on a full six hours early. The six days of normal light did nothing to offset the shock the mice suffered. The young mice demonstrated clear signs of mental instability, and as for the older mice? A full 53 percent of them simply died.

The problem, in this case, is the lack of a reliable sleep schedule. Although night shifts are inarguably worse for your health than day shifts, the real danger is trying to switch back and forth. Of course, you don't have to have such a severe shock as having to work a completely different shift for your schedule to get thrown completely off-kilter.

Getting up early for work on some days (especially if you aren't in the habit of getting to bed earlier) can cause negative health effects as well. So can shaking up your eating schedule, which throws off your blood sugar production without changing how your body is accustomed to burning it. And then there's the pesky problem of light — besides watching TV late into the night, we all carry around devices that we use to shine a bright white beam directly into our eyes at all hours of the day.

So what is there to do about it? Well, if you've got a schedule-shakeup coming on your calendar, try easing yourself into it by gradually shifting your sleep habits to fit your needs ahead of time, and give yourself time to adjust after you make the switch as well (also, try to keep that new schedule as long as possible, instead of switching back and forth). And shift your meals gradually as well, in order to keep all of your internal clocks in sync with each other as well as with the world around them.

When it comes to light, the only thing to do about it is to be aware of what you're exposing yourself to. Keep lights in your house dim after dark and try to limit your phone usage a couple of hours before bed. And here's one more tip from Susan Golden, director of the UCSD  Circadian Biology: when she and her husband watch TV late at night, they do so through orange-colored sunglasses. That keeps their exposure to the noon- blue light from the TV to a minimum.