What Are The Symptoms Of Dementia Or Alzheimers?

I know an older woman, in her 80's, who has been experiencing (5 to date) bouts of what seems like fugue..she comes to her senses and has no idea of what she has done, where she has been, etc. The last time, she woke up in the hospital with no memory of how she got there or why she was there at all. Are there organic causes of fugue states, or should the family be worried about dementia or alzheimers? In reading the signs of dementia and alzheimers, it seems that she has a few of the symptoms, but not all. Any ideas?