How does dementia start or progress?

My Mom now 84 and her health is declining, we go to the Dr. and have test done every week. It seems we always end up with the age related conclusion, Constant pain and now confusion is joining in. We know that there is nothing else they can do but make her comfortable, NOW she has started to have spells where she makes no sense, she called me and asked me what to do with a pill, (do I swallow it?) , this morning she wanted to know if she should drink prune juice or not? I thought oh no she is really loosing it, an hour later she is fine. Is this a normal progression of dimentia? She has spells of confusion and then gets very aggrevated, This confusion seems to be getting worse and she is aware and frustrated that her mind is not working right. Does dimentia come and go at first? Any advise is helpful,,, thank you all in advance for the support and sahring your experiences with me.. It helps to know what others are going through....