Benign Paroxysmal Positional Vertigo (BPPV): This condition is characterized by brief, episodic vertigo spells triggered by specific head movements, such as standing up quickly. The absence of orthostatic hypotension and a normal neurological exam supports this diagnosis, as BPPV does not typically cause systemic symptoms or abnormal neurological findings.

Vestibular Migraine: Although classically associated with headache, vestibular migraines can present with isolated vertigo episodes that may be triggered by positional changes. The normal neurological exam and lack of orthostatic hypotension do not rule out this diagnosis.
Meniere's Disease: Characterized by episodic vertigo, tinnitus, hearing loss, and ear fullness. While the question does not mention auditory symptoms, early stages of Meniere's might present with vertigo alone.
Anxiety-Related Dizziness: Anxiety can cause or exacerbate dizziness, especially in situations that trigger anxiety, such as standing up quickly. The normal physical exam does not exclude this possibility.

Cardiac Arrhythmias: Although orthostatic hypotension was not measured, certain arrhythmias (like sick sinus syndrome or atrioventricular block) could cause dizziness upon standing due to transient decreases in cardiac output. These conditions are critical to identify due to their potential for severe consequences.
Transient Ischemic Attack (TIA) or Stroke: While the normal neurological exam is reassuring, it's crucial not to miss a TIA or stroke, especially if the dizziness is accompanied by other focal neurological symptoms that might have been overlooked or are intermittent.
Multiple System Atrophy (MSA): This rare neurodegenerative disorder can present with orthostatic hypotension, but early in the disease, orthostatic changes might not be prominent. Other symptoms like parkinsonism, cerebellar ataxia, or pyramidal signs might develop over time.

Autoimmune Inner Ear Disease: An inflammatory condition affecting the inner ear, leading to vertigo, hearing loss, and sometimes tinnitus. It's less common but should be considered in patients with recurrent, unexplained vertigo.
Superior Canal Dehiscence: A rare condition where there's an abnormal opening in the bone overlying the superior canal of the inner ear, leading to vertigo and nystagmus triggered by sound or pressure changes.
Chiari Malformation: A structural defect in the cerebellum that can cause vertigo, among other symptoms, especially with positional changes. However, it often presents with other neurological signs and symptoms.