Dehydration: This is often the most common and straightforward cause of orthostatic hypotension, resulting from insufficient fluid intake, excessive fluid loss (e.g., diarrhea, vomiting), or a combination of both. Dehydration reduces blood volume, leading to decreased cardiac output and blood pressure when standing.

Medication Side Effects: Many medications can cause orthostatic hypotension as a side effect, including antihypertensives, diuretics, antidepressants (especially MAOIs and tricyclic antidepressants), and anti-parkinsonian drugs. These medications can either decrease blood volume or interfere with the body's ability to compensate for changes in blood pressure.
Autonomic Dysfunction: Conditions that affect the autonomic nervous system, such as diabetes mellitus, amyloidosis, or multiple system atrophy, can lead to orthostatic hypotension. The autonomic nervous system plays a crucial role in regulating blood pressure, and its dysfunction can impair the body's ability to maintain blood pressure when changing positions.
Blood Loss or Anemia: Significant blood loss (either internal or external) or severe anemia can reduce the total blood volume, leading to orthostatic hypotension. The body has less blood to circulate, and thus, less blood returns to the heart, reducing cardiac output and blood pressure.

Adrenal Insufficiency: Although less common, adrenal insufficiency (e.g., Addison's disease) is a critical diagnosis not to miss. It can cause orthostatic hypotension due to the lack of cortisol and aldosterone, which are essential for maintaining blood pressure and fluid balance.
Pheochromocytoma: Paradoxically, pheochromocytoma can sometimes present with orthostatic hypotension. This rare tumor of the adrenal gland can cause unpredictable blood pressure fluctuations, including orthostatic hypotension, due to the intermittent release of catecholamines.
Cardiac Conditions: Certain cardiac conditions, such as significant aortic stenosis, cardiac tamponade, or constrictive pericarditis, can lead to orthostatic hypotension. These conditions impair the heart's ability to increase output in response to standing.

Pure Autonomic Failure (PAF): A rare condition characterized by progressive autonomic dysfunction without other neurologic features, leading to severe orthostatic hypotension.
Dopamine Beta-Hydroxylase Deficiency: A rare genetic disorder affecting the synthesis of norepinephrine, leading to severe orthostatic hypotension due to the inability to adequately respond to postural changes.
Familial Dysautonomia (Riley-Day Syndrome): A rare genetic disorder that affects the development of the autonomic nervous system, leading to various symptoms including orthostatic hypotension.