Even though your son is 46, he still needs his mother. He is still your baby son. Ask him whats wrong and if he refuses to talk than observe him. see if you notice anything new or different in his life. If he hates it when you suggest to take a shower or to get back into the real world than make him answer to himself. instead of telling him, ask him. ask him with questions that'll make him think; think of his own answers to his own problems.
I've worked in group homes for adults with mental illness for 3 years. Your son needs you to be firm and set boundries and expectations. If you go soft on him he will only slip further. Be strong. I know it's difficult, but you know what is best for your son.