Dehydration: This is a common and often overlooked cause of sudden onset fatigue and hypotension. Dehydration can occur due to various reasons such as inadequate fluid intake, excessive sweating, or gastrointestinal losses. It is a likely diagnosis given its high prevalence and the nonspecific nature of the symptoms.

Anemia: A condition characterized by a decrease in the number of red blood cells or the amount of hemoglobin in the blood. Anemia can lead to fatigue and hypotension due to reduced oxygen delivery to tissues. It is a plausible diagnosis, especially if the patient has a history of menstrual abnormalities, gastrointestinal bleeding, or chronic diseases.
Hypothyroidism: A condition where the thyroid gland does not produce enough thyroid hormones, which are essential for energy production and maintaining blood pressure. Hypothyroidism can cause fatigue, hypotension, and other systemic symptoms.
Adrenal Insufficiency: A condition where the adrenal glands do not produce enough cortisol and aldosterone hormones. These hormones are crucial for maintaining blood pressure and responding to stress. Adrenal insufficiency can lead to fatigue, hypotension, and other symptoms.

Myocardial Infarction (Heart Attack): Although less common in women, myocardial infarction can present with atypical symptoms such as fatigue and hypotension, especially in postmenopausal women. It is crucial to consider this diagnosis due to its high mortality rate if left untreated.
Pulmonary Embolism: A blockage of an artery in the lungs that can cause sudden onset fatigue, hypotension, and shortness of breath. Pulmonary embolism is a life-threatening condition that requires immediate medical attention.
Septic Shock: A severe condition that occurs when an overwhelming infection leads to life-threatening low blood pressure. Septic shock can present with fatigue, hypotension, and other systemic symptoms.

Pheochromocytoma: A rare tumor of the adrenal gland that produces excess catecholamines, leading to episodes of hypertension, but can also cause hypotension and fatigue due to intermittent hormone release.
Addisonian Crisis: A life-threatening condition that occurs when the adrenal glands suddenly stop producing cortisol and aldosterone hormones, leading to severe hypotension, fatigue, and other symptoms.
Hemorrhagic Shock: A condition that occurs when there is significant blood loss, leading to hypotension and fatigue. Although rare, it is essential to consider this diagnosis, especially if there is a history of trauma or internal bleeding.