In my opinion, your brother is either suffering from an Anxiety disorder or a depressive illness with anxiety symptoms. It might be due to various forms of stress or triggers. He will require detailed assessment by a psychiatrist to arrive at a diagnosis and start treatment. If his condition is severe enough, then Psychiatrist can make recommendations about hostel stay or not but that only depends to specifics of the case. A certificate should be ideally issued by a psychiatrist only if a patient has been physically examined by them.
Next Steps
Consult a psychiatrist immediately