The knowledge that one may lose their normal 'selves' and become dependent also brings painful emotions and even depression or anger. Diagnosis may lead to denial of the problem or even relief at having identified the reason for symptoms.
Sometimes families and individuals try to hide the fact as it may be perceived as embarrasing or there may be some stigma attached to it. However it is better to be prepared. Legal, financial, domestic and family issues need to be resolved. An article from Johns Hopkins, Facing Dementia discusses some typical behaviours and reaction. Awareness is the first step to better management.