Without any delay, take him to a psychiatrist for assessment and possible treatment with medications. He could possibly suffering from an acute psychotic episode either instability of mood or disordered thoughts. If he is unwilling, take a legal route as it would be against his wishes.
Next Steps
Convince him to see a psychiatrist. if not, talk to a lawyer or even take the help of police who ate usually very helpful in these health related matters.
Health Tips
Psychiatrists or any of their team members visiting the house of a first time unbooked, undiagnosed patient is nor legal.