Dementia. Memory is required for orientation - you have to remember where you are! Memory & disorientation are part & parcel of dementia, although this can also be found in depressed patients who aren't paying attention to their surroundings. Delirious patients can also demonstrate memory loss & disorientation. Regardless, someone showing these symptoms needs to be evaluated.
Many possibilities. Could b serious--i'd check with your doctor and/or a neurologist.