What Is Orthostatic Hypotension?
Orthostatic hypotension (OH) — also called postural hypotension — is defined as a drop in systolic blood pressure of ≥20 mmHg or diastolic blood pressure of ≥10 mmHg within 3 minutes of standing from sitting or lying down. It occurs because, normally, standing triggers a rapid reflex response that constricts blood vessels and increases heart rate to maintain blood pressure against gravity. When this reflex is sluggish or overwhelmed, blood pools in the legs, brain perfusion drops, and you feel dizzy, lightheaded, or may briefly lose consciousness.
Who Gets It?
Orthostatic hypotension affects 5–20% of the general population but rises steeply with age — up to 30% of people over 70. It is common in hospital patients and a significant cause of falls in older adults.
Common Causes
Dehydration
The most common reversible cause. Reduced blood volume means there is less to redistribute when you stand. Hot weather, fever, diarrhoea, vomiting, or simply not drinking enough fluid can all cause acute orthostatic symptoms. Drinking 500 mL of water rapidly before standing (the "water bolus") can acutely raise blood pressure by 10–15 mmHg.
Medications
Blood pressure medications (especially alpha-blockers like tamsulosin used for prostate symptoms, and ACE inhibitors), diuretics, antidepressants (tricyclics, SSRIs), antipsychotics, and nitrates are common pharmacological causes. Symptoms are often worst in the morning or after large meals (postprandial hypotension).
Prolonged Bed Rest or Inactivity
Even a few days of bed rest causes deconditioning of the cardiovascular reflexes. Hospital patients are particularly vulnerable.
Autonomic Nervous System Disorders
In more severe or persistent OH, the autonomic reflex arc is damaged. This occurs in Parkinson's disease and its related conditions (MSA, Lewy body dementia), diabetic autonomic neuropathy, and pure autonomic failure. These conditions require specialised management.
POTS (Postural Tachycardia Syndrome)
A related but distinct condition primarily affecting young women (often post-viral, including post-COVID): standing triggers an excessive heart rate increase (≥30 bpm within 10 minutes) rather than a large blood pressure drop. Symptoms include lightheadedness, palpitations, brain fog, fatigue, and sometimes near-fainting. POTS is significantly underdiagnosed.
Practical Management
- Hydrate adequately — 2–3 litres of water daily, including a large glass before getting out of bed in the morning
- Increase salt intake (unless you have hypertension or heart failure) — 6–10 g/day of sodium helps retain fluid volume
- Rise slowly — sit at the edge of the bed for 30–60 seconds before standing; avoid sudden position changes
- Compression stockings — knee-high or thigh-high graduated compression (20–30 mmHg) reduces venous pooling
- Review medications — discuss with your doctor whether any drugs can be adjusted or timed differently
- Avoid alcohol, large meals, and prolonged standing
- Exercise — recumbent cycling or swimming builds cardiovascular conditioning without prolonged upright posture
When to See a Doctor
Occasional mild dizziness on standing is common and often benign. See your doctor if you faint (syncope), if symptoms are severe or worsening, if they persist despite adequate hydration, or if accompanied by other neurological symptoms — these may indicate an underlying autonomic disorder requiring formal tilt-table testing and specialist evaluation.