Well, you shouldn't blow off work like that, but sometimes we all need mental health days. Vomiting and diarrhea, or sometimes both in combination are pretty good. Generally, they will work for getting a day off, without your employer wanting documentation...in the form of a doctor's excuse.
Likewise, if you are at work, you've been there about 3 hours or so, and you know that you won't be able to survive the rest of the day, having the runs will get you a "get out of work free" card. You run to the bathroom. You come back. Your run to the bathroom 10 minutes later. You come back. Another 15 minutes, another run to the bathroom. At that point you tell the boss, "I've had to run to the bathroom 3 times in the past hour, and I can feel #4 coming on. I really need to go home."
Generally, that works. Since you're running to the men's (or women's) room and going into one of the stalls, there's nobody that can say you weren't pooping your guts out. And having the skitters very rarely causes any external signs of illness....no fever, no flushed face, no paleness, etc.