What makes mood change in the elderly?

My mom's moods have gone from normal to hateful in a matter of minutes. She is 83 and started crying saying no one loves her. She wants to go back home to her home. She thinks we are stealing her jewelry. She doesnt remember who she talks to or who visits. She has had min strokes before but, now she is on lots of blood thiner. I just don't know. Idea's?