You most likely have a condition called benign parxosymal positional vertigo.
Benign means the condition is bothersome but not serious. Paroxysmal means the symptoms come and go. The symptoms are brought on by head movement. Keeping your head still should rapidly stop any dizziness you feel.
Symptoms can be quite mild, with just a few seconds of a spinning or off-balance sensation when the head moves a certain way. But some people experience severe dizziness, along with nausea and falling.
The condition is caused by a problem in one of our two internal "gyroscopes." There is one in each ear. Each gyroscope is actually a complex set of canals filled with fluid. In parts of the canal system, cells with hair-like structures coat the inside lining. The "hairs" are paired up with tiny stones (called otoliths). When working normally, the otoliths move in the fluid in response to our head movement. This moves the hairs, which triggers the cells to send signals to the brain. The brain processes these signals and sends messages to our eyes and body. This is how we can remain steady without feeling dizzy.
Sometimes, one of these otoliths breaks loose and moves within the fluid. It can settle in a place it shouldn't be. Depending where it ends up, it can confuse the hair cells in this other location. Incorrect signals are sent to the brain if our head moves in a certain way. The result is benign parxosymal positional vertigo.
Your doctor (or an Ear, Nose and Throat specialist) may be able to move your head in specific ways to free the misplaced otolith. The symptoms can improve and often go away completely. The freed otolith does not usually move to another spot.
Call your doctor's office to arrange an appointment. He or she may be able to do the head maneuvers in the office. If not, your doctor can refer you to an Ear, Nose and Throat professional experienced in these maneuvers.