We think of two different things when we talk about 'mental' anything. First is the physical organ we call the brain. It can be ill just like any other part of our bodies. The other thing we talk about is the mind. It is not physical and therefore the word illness takes on a very cloudy definition.
Many people get a diagnosis of mental illness and are given drugs to treat it.
God is the answer. He created us and we have a need for a relationship with Him. Our problems are spiritual unless they are physical. Have nothing to do with them. So many people claim to be Christians, but they deny God's power.