Do I really need to worry about food poisoning?

You do if you want to avoid those nasty bouts of cramps, diarrhea, and vomiting. The fact is that most every time you have a "stomach flu" or even a stomachache, food poisoning bacteria are the likely culprits. What's more, you may never know what hit you, since symptoms generally take up to two days to appear. Even mild complaints like fatigue, dizziness, and muscle aches are probably caused by tainted food a lot more often than you realize. Bacteria in food can double in number every 20 minutes at room temperature, and a few thousand is all it takes to lay you low.

Where do bacteria come from?

You can't see, smell, or taste them, but millions of bacteria are all around you. Most are harmless; some, like E. coli and salmonella, are a menace to your digestive system. These bugs may already be present in raw meat, poultry, fish, or eggs -- they thrive on protein -- or you may introduce them yourself if you forget to wash your hands before handling food. They will be happy to infest any kind of food as long as it's moist and warm enough and not too salty or acidic.
These bacteria can greatly effect your stomach and give rise to food poisoning.

Won't cook kill bacteria?

Cooking food to 160 degrees Fahrenheit will kill most bacteria. (Some meats need to be even hotter. Don't guess by the color; use a meat thermometer.) But if the food has been at room temperature for more than two hours, bacteria may have accumulated to dangerous levels and formed heat-resistant toxins that cannot be killed by cooking. Even cooked food can become contaminated this way, so get those leftovers into the fridge as soon as you can.
To avoid food poisoning and other complaints like fatigue, dizziness, etc., be careful about these bacteria.