Dementia describes a group of symptoms affecting memory, thinking and social abilities severely enough to interfere with your daily life. It isn't a specific disease, but several different diseases may cause dementia.Though dementia generally involves memory loss, memory loss has different causes. Having memory loss alone doesn't mean you have dementia.Alzheimer's disease is the most common cause of a progressive dementia in older adults, but there are a number of causes of dementia. Depending on the cause, some dementia symptoms may be reversible.Individuals may need help getting dressed and combing their hair. They may also show significant changes in personality; for instance, becoming suspicious or agitated for no reason. There are also likely to be sleep disturbances.Severe dementia: at this stage, symptoms have worsened considerably. There may be a loss of ability to communicate, and the individual might need full-time care. Simple tasks, such as sitting and holding one’s head up become impossible. Bladder control may be lost.