You wake up one morning with a swollen right hand and a tingling sensation. You don’t remember suffering any injury, and have no idea what might have caused it. What do you do?

If you’re like many American "cyberchondriacs" (about 160 million in all), your first step is to get online and try to match your symptoms with diseases and conditions listed in databases maintained by a variety of health and medical websites, such as WebMD or Everyday Health. Increasingly, people are using this kind of information to make healthcare decisions, especially whether their symptoms are worrisome.

Keep in mind that, although these Web-based tools can provide you with useful information about a possible problem, a website is no substitute for a doctor’s knowledge, which is backed up by years of education and experience. Self-diagnosis and self-treatment based on something you read online is not a good idea… and could be potentially fatal.