IBS is not a dangerous disease. It causes no harm to your system. It can, however, be quite uncomfortable or even downright painful. The underlying cause appears to be inappropriate tightening of the muscles in the colon. When they contract too slowly or too weakly the stool slows down leading to constipation.
Diagnosis is made by history.
There are no tests that will reveal any positive results. On the other hand, usually tests have to be performed in order to make certain the symptoms are not being caused by a more serious condition like colitis or cancer or diverticulitis. These tests may include such things as evaluation of a stool sample, Xrays, and direct examination of the colon through a scope. Additionally, there are medications that can be of some temporary value with the painful symptoms of the acute attack. For more information go to the Crohn's Disease, Ulcerative Colitis, IBS server FAQ .