hi i had gone through your query and understand your concerns. i would come up with the possibility of POST HEPRETIC NEURALGIA
may be the cause for your father sufferings.
-in such cases i would suggest you taking Homeopathic
medicines gives safe and permanent cure for your father complaints
-Usually in such cases I will give treatment for my patients in the following manner VARIOLINUM is the homeopathic medicines is usful in sch cases with excellent result
-consult your local homeopathic physician for correct diagnosis of the case and remedy to fit his complaints
I hope this is helpful for you, thank you