Signs of loss of function include:

• Numbness, loss of all feeling, or inability to move part or all of one side of the body (paralysis).
• Confusion or altered behavior, such as the inability to fully rouse a person from sleep, or unusually aggressive or combative behavior.
• Sudden dimness, blurring, loss of vision in one or both eyes, or double vision.
• Inability to speak, difficulty speaking, or difficulty understanding speech.
• Inability to or difficulty walking or standing (ataxia).
• Headache, which is severe and in a specific area, without another apparent cause.
• Dizziness or loss of balance with nausea or vomiting.
• Fainting or loss of consciousness.

A temporary loss of function can have many causes, such as a minor injury to an arm or leg, stress, or a more serious problem, such as a seizure. Most people have felt a leg "fall asleep," causing a pins-and-needles sensation, and then quickly return to normal after some movement or change of position.

Most of the time the cause of a temporary loss of function is not so obvious and may be serious. Loss of function, even for a few minutes, may indicate a decrease in blood flow to the brain. Vertigo or lightheadedness may occur before a:

• Stroke, which can cause progressive and permanent loss of function. Call 911 or other emergency services immediately if you suspect a stroke is occurring.
• Transient ischemic attack (TIA), which causes a brief and temporary loss of function. Even though function returns after a TIA, the TIA is a warning sign that a stroke may soon occur. The first TIA needs to be treated as an emergency. A TIA may mean that you have an increased chance of having heart disease or a heart attack.

Prompt medical attention is required for anyone with signs of loss of function, even if the loss of function is brief and temporary.