The disease, which is popularly called "crystal shift" and thought to be the main cause of dizziness, is actually defined as positional vertigo (Benign positional paroxysmal vertigo). Normally, we all have crystals in our ears. While these crystals are located in a gel layer on the hair cells in the structures we call the utricle and saccule, they are not located in the semicircular canals. If these crystals somehow escape into the semicircular canals, the patient becomes dizzy. Typically, this dizziness occurs with sudden head movements. It lasts as little as seconds, it can be very severe, it can be accompanied by nausea and vomiting. Among the known causes of this disease are blows to the head, prolonged bed rest, and some ear surgeries.

 

Source:  http://www.kbb.org.tr