My grandmother had Alzheimer. I don't remember much from the development because I was very young at the time. I do remember going to my grandfather and grandmother with my brother (they lived 200 meters from my parents house so I walked to them pretty often) and my grandmother didn't recognize us so she wanted us to leave. She tried to hit us and my grandfather had to stop her. This ofcourse was devastating for him to see his wife trying to scare their grandchildren away.
I also remember that the one moment her memory was clear and the next it wasn't. It comes and goes which is very strange. In the case of my grandmother, the progression from the first signs until she passed away took about 4-5 years.