Orthostatic Hypotension: This condition is characterized by a significant drop in blood pressure when standing up from sitting or lying down, leading to symptoms like lightheadedness. It is common in the elderly due to age-related changes, dehydration, or medication side effects.

Dehydration: Inadequate fluid intake or excessive fluid loss can lead to hypotension and lightheadedness, especially in older adults whose sense of thirst may be diminished.
Medication Side Effects: Many medications, including antihypertensives, diuretics, and certain antidepressants, can cause hypotension as a side effect.
Autonomic Dysfunction: Conditions affecting the autonomic nervous system, such as diabetes or Parkinson's disease, can disrupt blood pressure regulation.

Cardiac Conditions: Although less likely, conditions like heart failure, significant valvular disease, or cardiac arrhythmias can cause episodes of hypotension and must be considered due to their potential severity.
Neurological Disorders: Rare neurological conditions, such as multiple system atrophy or pure autonomic failure, can cause severe orthostatic hypotension.
Adrenal Insufficiency: This is a life-threatening condition that can cause hypotension among other symptoms, and although rare, it must not be missed.

Pheochromocytoma: A rare tumor of the adrenal gland that can cause episodes of hypertension but occasionally presents with orthostatic hypotension.
Vasovagal Syncope: Although more commonly associated with a sudden loss of consciousness, it can sometimes present with pre-syncopal symptoms like lightheadedness.
Mitral Valve Prolapse: In rare cases, this condition can lead to hypotension, especially if there is significant mitral regurgitation or if the patient has a high-output state.