Is misidentification typical of delusional problems with dementia or sleep issues?

When my mom misidentifies my dad as someone else, like her father, she then feels that my dad left her alone, or has gone away. When she suddenly "sees" my dad for who he is, he then gets heck for going away. She always seems to "see" him as someone she is terrified of, like her own dead father. So she feels if my dad would just stay home, these others would not show up. In reality my dad doesn't go anywhere, never has. In this scenario he is in a no win situation. This occurs most days for one to several hours, mostly at night or after a period of sleep. She's nearly 80, in good health, fair memory, early vascular dementia, but extremely anxious. No medications except Xanax when needed. Awaiting new doctors and visits soon, winging this in our own.