The spirit is the real you. Your inner man, if you will. The mind is a part of the soul. The soul is what we need to express the inner man. For example, you have a desire in your inner man to go on a holiday. Let's say Hawaii. You will have to do a lot of stuff to get there - and your mind will be needed to plan, organise fares, travel documents and everything that has to do with the trip.
If you are born again, Lord Jesus lives in your spirit man, not your mind. If you have proper fellowship, pray, study the Word and meet with other believers,your spirit man should be in good shape. If not, you will suffer "spiritual malnutrition". Lord Jesus said that His words are spirit and life. "Daily Bread" is the living word for the spirit man, not food for the body.
The mind should serve the spirit, not the other way around. If the mind is troubled, preoccupied with life issues, full of false notions or unrenewed, it becomes a hindrance rather than a help. Very often, mental health issues are induced by attacks from evil spirits. They can implant suggestions into you mind that are contrary to God's word. They can be positive or negative. It usually fits the individual's personality. An introvert is likely to be attacked with negative thoughts, hopelessness and a sense of failure. The outgoing type is more likely to be influenced by presumption masquerading as faith. The devil will use God's word. For some he will trap them in an endless cycle such as Paul went through in Romans 7. For others, he will incite them to some action or word that is contrary to God's will. Peter is a classic case. He rebuked Lord Jesus for saying that he was going to Jerusalem to be killed. Lord Jesus said, "Get behind me, Satan". We see there an example of an evil thought being planted and then spoken out. A similar incident is Peter's boast that he would never betray the Lord Jesus.
An unhealthy mind is one that is constantly bombarded with alien thoughts or not able to think at all. It may be a chemical imbalance or an illness. If so, the correct medication will solve the problem. Serious illness can affect the mind. But we need to be aware of the possibility that our minds are under attack. This is absolutely normal for Christians. It is the war that all Christians are engaged in. It's what Paul spoke about in 2 Corinthians 10:5