Hypovolemia: This is often the most common cause of unexplained hypotension, resulting from decreased blood volume due to dehydration, bleeding, or other fluid losses. It's a straightforward and common condition that can lead to hypotension.

Sepsis: An infection that leads to a systemic inflammatory response can cause vasodilation and hypotension. Given its prevalence and potential severity, it's a likely diagnosis to consider.
Cardiogenic Shock: Conditions like myocardial infarction or heart failure can lead to inadequate cardiac output, resulting in hypotension. This is a common and serious cause of hypotension.
Anaphylaxis: A severe allergic reaction can cause widespread vasodilation and increased vascular permeability, leading to hypotension. Although less common than other causes, its potential for rapid progression makes it a significant consideration.

Adrenal Insufficiency: Although rare, adrenal insufficiency (e.g., Addisonian crisis) can cause hypotension due to the lack of cortisol and aldosterone. Missing this diagnosis can be fatal.
Pulmonary Embolism: A large pulmonary embolism can lead to hypotension by obstructing blood flow through the lungs, reducing cardiac output. Its potential for sudden onset and high mortality rate makes it a critical diagnosis not to miss.
Toxic Ingestions: Certain drugs or toxins (e.g., beta-blockers, calcium channel blockers, or tricyclic antidepressants) can cause hypotension. Given the variety of substances and the potential for severe outcomes, these should not be overlooked.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodic hypotension due to the release of catecholamines, although it's more commonly associated with hypertension.
Autonomic Dysfunction: Conditions affecting the autonomic nervous system, such as autonomic neuropathy or pure autonomic failure, can lead to orthostatic hypotension. These are less common but should be considered in the appropriate clinical context.
Endocrine Disorders: Other endocrine disorders, such as hypothyroidism or diabetes insipidus, can occasionally present with hypotension, though they are less common causes.