Check for serious household/workplace toxins such as radon, asbestos, and formaldehyde. Asbestos is most often found in basement pipe insulation. Radon is a naturally occurring radioactive gas emitted from the ground. Kits are available to test your home for radon. Formadehyde can be found in home building materials and out-gassing toxic fumes. Check out the Environmental Protection Agency's web site for more information:

http://www.epa.gov