If not taken care his condition will become more critical an worse.
Emotional and mental illness should be treated like physical health issues so kindly check out a psychologist or psychotherapist near you he/ she will surely help you out.
Talk with your brother take care of his Diet spend some time with him listen to him.ask him why he feels so negative.family support helps in such cases.
Next Steps
patient is not in the state to help out himself.so family should take initiative to take him out from this condition.
Health Tips
Don't show disrespect to the patient.listen to him ,give his response when needed what ever he is saying is what he is feeling these are the symptoms of his ill-health( mental)
so don't get angry with him .he needs help.