Thanks for your question on Health Care Magic.
I can understand your father's situation and problem.
Cancer wherever in the body, produces chemical mediators called as chemokines. These are responsible for decreased appetite.
Burden of these mediators is high if cancer is metastatic.
Because your father is having metastatic cancer, he is having marked loss of appetite and
weight loss.
For his headache and confusion, loosing speech etc, possibility of
brain metastasis is more.
So better to get done
MRI brain to rule out brain metastasis.
Another possibility is electrolyte disturbance like low sodium. So also get done serum sodium level.
If brain metastasis is present than radiotherapy and
chemotherapy are the options.
Survival rate in such type of metastatic cancer is very low, less than 1 year.
Hope I have solved your query.
Wishing good health to your father. Thanks.