Thanks for your consult at DoctorSpring.com.
I have gone through your question in detail and I can understand what you are going through.
I am very sorry to hear about your brother in law. Well its difficult to pin point the exact cause but as you said that your brother in law developed symptoms over just 10 days and before 10 days he was all right, the diagnosis goes in favor of Psychosis, probably a Brief Psychotic Disorder. For the illness to be schizophrenia, the symptoms had to persist for at least 1 month. Hence officially it cannot be a diagnosis of schizophrenia but there is a good chance that the same could have progressed to schizophrenia. For psychotic depression,there are mostly a long term depressive symptoms before 10 days and then gradually the psychotic symptoms start. If he was fine 10 days back, then probably the illness has to be a Brief Psychotic Disorder.
All said the psychiatrist or Doctor who had examined him personally should be the best person to comment on the diagnosis.
Hope I am able to answer your concerns.
If you have any further query, I would be glad to help you. In future if you need any help, you can always utilize services of Doctor Spring.
Wish you good health,
Dr. Srikanth Reddy M.D.