Unlike depression or anxiety the Bible says nothing specific about psychosis. However, in Daniel chapter 4 there is a description of a psychotic disorder called boanthropy.
You are most likely familiar with the story. Nebuchadnezzar, King of Babylon, has a dream about a great tree being cut down that he is unable to understand. He calls the magicians, diviners and wise men of his kingdom together but they are unable to explain the dream to him. Finally, the prophet Daniel appears on the scene and interprets the dream for the King. Daniel tells Nebuchadnezzar that because of his sin, God is going to remove his kingdom from him for seven years. He will do this by changing Nebuchadnezzar’s mind from that of a man to that of a beast, specifically an ox. The King will be driven away from mankind, eating grass and living out in the elements. And that is exactly what happens. For seven years, Nebuchadnezzar believes himself to be an animal. In the seventh year of his delusional state, Daniel 4:34 tells us that Nebuchadnezzar’s “reason returned” to him and he blessed, praised and honored the Most High.
Now you may have never thought that this was a mental illness, but it is and it still occurs today. As I said above, it is called boanthropy when the person, in a delusional state, believes themselves to be an ox or cow. It is called lycanthropy when they think they are a wolf (this may be where we get our legend of the werewolf). There are many other variations depending on the animal. But the basic symptom is a delusional state such that the person believes themselves to be an animal and begins to live and behave that way. In this particular instance God used the mental illness as discipline, but we should not generalized that to every case of mental illness. While God certainly could choose to bring mental illness into our lives as discipline (Deuteronomy 28:28), if we were to mistakenly generalize that it is always the result of God’s discipline then we would also have to consider common problems such as boils, scabs, itching (Deuteronomy 28:27) and tumors in the groin (hemorrhoids; 1 Samuel 5:9) to always be signs of God’s discipline.
As people of faith, what can we learn from this story about delusions? I believe that Daniel 4:34 gives us an amazing truth that we can apply to those with delusions. Nebuchadnezzar was not able to bless and praise the Most High until his “reason returned” to him. In other words, until his hallucinations and delusional state were removed. Hallucinations and delusions can disconnect an individual from the reality of acknowledging God. As those ministering to individuals with hallucinations and delusions we should guide them towards treatments (e.g., antipsychotic medication) that will effectively minimize or remove these symptoms so that the individual, through pastoral care, can re-connect with the Father.