(HealthDay News) -- Fainting can occur for a number of reasons, from feeling terror to being dehydrated, a state in which the body does not have as much fluid or water as it should. In some instances, fainting requires emergency medical attention.

The ADAM Encyclopedia lists these warning signs of dangerous fainting:

• Fainting and falling from a height, particularly if there is bleeding or other injury.
• Not regaining alertness within a few minutes.
• Fainting when someone is pregnant or has diabetes, or is older than age 50.
• Fainting accompanied by pain or pressure in the chest.
• Fainting accompanied by changes in heartbeat or signs of stroke, including changes in speech, vision and the ability to move both sides of the body.
• Fainting that causes convulsions, an injury to the tongue or the inability to control the bowels or bladder.