What Causes Irrelevant Speaking Of An Elderly Person?

HI my mother is 68 years old . Recently since last 2 days she is talking ireelevant things Like for EXAMPLE she talks normally and suddenly her tone of voice becomes slow and she start speaking irelevant things like some is standing beside some one is working there, this is happending since last 2 days . mayh i know whats the reason behind this and if there is any treatment to cure this completely Please help me iam really tensed and worried