It occurs over a long period of time. There are many causes of dementia including Alzheimer's Disease, strokes, longterm alcohol abuse, a reaction to medication, Vitamin B12 deficiency, thyroid disease and depression. Symptoms and duration of dementia can be months to years. Usually speech remains normal. Generally attention is normal, although the person usually shows signs of difficulty in finding the right words.
Recent memory is impaired.
The older person's motor abilities remain normal until late in the disease. The individual's mood may be apathetic and there can be a loss of impulse control. Emphasis needs to be placed on the word sudden. This condition can be extremely serious and require immediate medical attention to prevent any permanent damage. Disturbances in sleep cycle are also a sign.