The term [nystagmus] is derived from the Greek word [νυσταγμένος], (nystagm?nos) meaning "sleepy" or "dizzy". It refers to the sensation of dizziness when you are just awakening from a deep sleep.
In medical terminology nystagmus refers to the rapid, usually lateral, movement of the eyes. This movement has a slower component that moves en eye to one side with a secondary rapid component that brings the eye to the starting point. Nystagmus eye movement is usually bilateral and can be unilateral in rare cases.
Nystagmus is a normal capability of the human visual system where the eyes move slightly to change the location of an image on the retina to avoid fatigue of the retinal components. In some individuals this movement is quite visible but it does not cause a problem and is called physiological or congenital nystagmus as shown in the video..
When nystagmus is pathological it can be the cause for vertigo, as the patient feels that the world is moving, when only the eyes are doing so. This can be caused by a pathology in the abducens nerve system.
Nystagmus can be triggered by using warm fluids in the external ear that will cause flow of the fluid in the semicircular canals of the inner ear. You can also see it if you turn a person around in a swiveling chair for a few turns and then stop and watch their eyes. You will see the rapid nystagmus movement of the eye. If you do this experiment, please be careful, as a person with nystagmus will have poor balance and they can fall with potential for injury.
Thanks to Lashkyrie for the use of her video on YouTube.
Note: The links to Google Translate include an icon that will allow you to hear the Greek or Latin pronunciation of the word.