Answer: Greta is suffering from Lewy body neurocognitive disorder /lewy body Dementia.
Explanation:
Lewy body neurocognitive disorder is a type of accompanied dementia disorder characterized by repeated visual hallucinations instability in blood pressure and heart rate, poor regulation of body temperature cognition, and the autonomic disfunctional nervous system, etc, It is a progressive disorder which is diagnosed when there is a decline in cognitive abilities which interferes with normal functioning. a common factor of this disorder across people is REM sleep behavior disorder, in which individuals tend to act out their dreams during sleeping.
Greta is probably suffering from Lewy body neurocognitive disorder because she is 81 years old and having symptoms characterized with the disorder in terms of experiencing vivid hallucinations, losing attention and behaves inappropriately, as if she has no inhibitions etc.
