Forgetfulness is possible for every human of any age who lives in high stress. Of course you can forget where you put your keys, but you will not put them in the dishwasher as a dementia patient may. Or you can forget about both the past and the recent events; whereas an Alzheimer’s patient remembers the distant past as if it’s today, while forgetting the recent period.
A forgetful person is disturbed by this forgetfulness and is in search of a remedy; whereas a demented patient is no longer uncomfortable about this subject, only the people around him and those who love him are complaining. A forgetful person tries to take some notes and put them in an order so as to remember, whereas a dementia patient does not even need to take notes anymore.