Signs of loss of function include:

• Numbness, loss of all feeling, or inability to move (paralysis) in part or all of one side of the body, such as the face, arm, and leg.
• Confusion or a change in behavior, such as the inability to fully rouse the 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.
• Sudden inability to walk or stand, or difficulty with walking or standing (ataxia).
• Headache (severe and in a specific area) without another apparent cause.
• Dizziness (vertigo) or loss of balance with nausea or vomiting.
• Fainting (syncope) or loss of consciousness.

True weakness is a lack of physical or muscle strength and the feeling that extra effort is required to move your arms, legs, or other muscles. If your muscle weakness is caused by pain, you may be able to make your muscles work, but it will hurt.

Weakness in one area of your body and loss of function, even for only a few minutes, may occur with a decrease in blood flow to the brain. This type of weakness may occur with a stroke or a transient ischemic attack (TIA). Early symptoms of a stroke and TIA can be the same and usually start with signs of loss of function.

• A stroke may cause a progressive and permanent loss of function. Call 911 or other emergency services immediately if you suspect a stroke is occurring.
• A transient ischemic attack (TIA) can cause a temporary loss of function. TIA symptoms usually go away after 10 to 20 minutes, but they may last longer. If a TIA lasts longer than 20 minutes, call 911 or other emergency services immediately.

Other medical problems that can cause temporary weakness or weakness that comes and goes include multiple sclerosis, electrolyte imbalances, herniated disc, myasthenia gravis, or a seizure disorder.

Prompt medical attention is required if someone has signs of loss of function, even if it is brief and temporary.