Yes, you should be concerned, and you should see your dentist immediately.
Bleeding is typically a sign of gum disease (also known as periodontal disease). Gum disease starts as mild gingival inflammation and can progress to more advanced stages. Healthy gums do not bleed with brushing and flossing.
Too many people who have gum disease have no idea they have it. Because it is often a silent disease that begins painlessly, the American Dental Association estimates that almost 50 percent of adults age 30 and up have some form of gum disease.
If you think you might have gum disease, you need to seek treatment immediately. More and more research links unhealthy gums to a host of other health problems, including an increased risk for diseases such as diabetes, heart disease, and some types of cancer.
Most gum disease can be prevented if diagnosed and treated early; however, more advanced stages can often cause irreversible damage. Be sure to have your teeth and gums checked regularly to prevent problems from gum disease. Be sure to stay current with your bi-annual visits to the dentist for examinations and cleanings. Tell your dentist if you have noticed bleeding while brushing and flossing your teeth.