What Causes Sudden Memory Loss In An Elderly?

My Mom went out to lunch today (quadruple bypass patient ,on coumadin and metformin ,was feeling pretty much normal til she got home around 2pm ,I bought Pizza today and she ate like 3-4 pieces 3:30-4:30pm and around 5- 5:30 she was dozing off (unusual) so I woke her and she was pretty much cognizant ,but them could not end her sentences correctly ...checked her blood sugar and it was at first 177 ,then checked it again on another monitor and it was 190 ! she has been able to walk and talk up until bedtime 8:30 and still says she s fine but still can t remember my birthday or her own ,can t finish a sentence and said she has not had a headache or numbness anywhere ..yet her speech is not right and memory is still not there ....