Hypochondria is a condition where the person is so overly obsessed with their health that they begin to believe that they are sick with a serious ailment even after having a medical evaluation that proves otherwise. A person with this condition is typically called a hypochondriac.
Usually the person doesn’t get satisfied with any of the statements not even of the doctor or the reports. He wants the assurance again and again. It's a very real condition that affects all genders and age groups equally. Diagnosis typically takes 6 months to determine and is usually made after the person has been checked completely and given a clean bill of health repeatedly, but yet continues to fear that they are sick.

Symptoms of hypochondria are constant anxiety over minor aches and pains that are considered to be normal. The anxiety is over the person thinking the minor aches and pains are a serious life threatening illness even though there is nothing physically wrong with them.
The condition can be better understood with the help of an example.  Suppose a person with reoccurring headaches will think that the headache is being caused by a brain tumor. The doctors will do scans and tests but the person will still believe that there is something wrong. They will either insist that the scans missed something, or that their headaches are caused by some other life threatening condition like a stroke. The person will then go through more tests and may even change doctors to have them reexamined because they are convinced that the headaches they are having are caused by something that is going to harm them.
Today, the treatment for this problem exists. A psychiatrist may be very helpful. Usually the treatment for hypochondria is a slow process that takes time. There are medications to help with the anxiety. Some people have lessened anxiety after finding out they aren't as sick as they thought and that they are just hypochondriacs.