Does anybody know why some days a person with dementia can be lucid and fairly normal and then the next day be completely phased out, not bothered about anything, anxious and defensive. I understand the disease affects and wipes out parts of the brain but what I dont understand is why some days it is not so bad and then other days it is awful. If some parts of the brain are dead why do they revive themselves on occasions? I just can't get my head around this disease or is that the nature of it?