See vertigo for a general approach
50-85% Sensitive for<unk> 
Patient sits upright
Patient's head is rotated to one side by 45 degrees. Then quickly lie the patient down
Maintain the head in 45 degree rotation but also 20 degrees of extension off the end of the table.
Observe the eyes for 45 seconds for nystagmus.  There is often 15 seconds of latency prior to symptoms.
Immediate symptoms requires consideration for central etiology
A positive test for<unk>  is evidenced by the rotational (torsional) nystagmus
Fast phase of the rotatory nystagmus is toward the affected ear (geotropic nystagmus), which is the ear closest to the ground
Rotational nystagmus away from affected ear (ageotropic nystagmus) requires consideration for central lesion
Immediate symptoms requires consideration for central etiology
Fast phase of the rotatory nystagmus is toward the affected ear (geotropic nystagmus), which is the ear closest to the ground
Rotational nystagmus away from affected ear (ageotropic nystagmus) requires consideration for central lesion
Concern for Cervical Artery Dissection
Cerebrovascular disease
Concern for vertebrobasilar insufficiency, See Stroke syndromes
Spinal injury
Cervical spondylosis
Benign paroxysmal positional vertigo
Vestibular/otologic
Vestibular neuritis
Benign paroxysmal positional vertigo 
Labyrinthitis
Traumatic 
Cluster headache
Infection