Hypotension is the medical term for low blood pressure, which is considered to be under 90/60. Usually, borderline-low or slightly low blood pressure readings produce no symptoms and may require no treatment. Low blood pressure can be a sign of good health in some people with no symptoms (e.g., athletes). It indicates that the hearts, lungs and blood vessels are well conditioned and in good working order. However, it may also be an indication that the body is unable to properly regulate blood pressure. In these cases, low blood pressure may require treatment.

There are a number of forms of low blood pressure that require medical diagnosis and treatment. The two most common are orthostatic hypotension and neurally mediated hypotension (NMH).

Orthostatic hypotension
Also called postural hypotension, orthostatic hypotension is a condition that is more likely to develop in people as they age. Therefore, it is often found in elderly patients. It may complicate the treatment of essential or isolated systolic hypertension (high blood pressure) because many patients with orthostatic hypotension also suffer from systolic hypertension when seated. Orthostatic hypotension is characterized by the body's inability to quickly regulate blood pressure after changes in position. People who have this condition may feel temporarily light-headed after standing up or rising from a lying position. People who suffer from this condition are counseled to change position gradually: sit before standing, and stand before walking. The patient's medication will usually be re-evaluated or altered depending on their symptoms.

A related form of hypotension is known as postprandial hypotension. This form of hypotension occurs between 15 and 90 minutes after people eat. It is more common among elderly patients.

Patients with orthostatic hypotension should avoid going for long periods without food or drink, and to avoid spending too much time in the sun. Fatigue, alcohol and heavy meals add to the likelihood and severity of these symptoms. Support stockings, increased salt intake, increased fluid intake and certain medications may help to alleviate the symptoms.

Neurally mediated hypotension (NMH)
Also known as neurogenic orthostatic hypotension, neurally mediated hypotension (NMH) is a condition in which the body does not regulate blood pressure well, especially when the person is upright. The condition often develops in young patients without heart disease who have hypotensive symptoms. It is thought to be a result of a communication problem between the brain and the nerve sensors that control blood pressure and heart rate.

In some cases, NMH is temporary and not serious. For example, a person may faint (vasovagal syncope) in certain situations such as after seeing blood, hearing bad news or getting an injection. Individuals may become pale and clammy, nauseous or develop an uncomfortable feeling in their stomach.

In other cases, NMH is more serious than orthostatic hypertension. People may have great difficulty or even an inability to stand for long periods of time. Other symptoms include dizziness, weakness, sweating, blurring of vision and near-fainting. Diagnosis hinges on ruling out other conditions, certain diagnostic tests (e.g.  electrocardiogram, tilt table test).