OK - I chose several answers, and some may seem contradictory to each other, so I'll explain.
*Mental illness cannot be "cured" through Christianity.
*Some people are unnecessarily medicated because they fake mental illness for attention.
*Mental illness can be faked.
*Medication and/or institutionalization is best for mentally ill patients
True mental illness cannot be cured just by becoming a Christian. True mental illness is not just a manifestation of the "mind" but rather a disease of the brain. There have been incredible advances in medicine and studies over the years that show there are differences in brains of people with Clinical Depression, Bi-Polar, Schizophrenia, Autism, etc. They can show differences in CT scans, in seratonin levels, in hormone levels, etc. The brain is still not fully mapped yet - God created an amazingly complicated "machine" when he created the human body - especially the brain. So as we learn more about how the brain works, we will come closer to being able to curing more and more of these diseases rather than just controlling them.
I am sure some people DO fake mental illness in order for attention. That is why psychiatrists are needed. Mental illness has become a very popular defense for criminals to try to use for commiting heinous crimes. It takes a professional to see to the truth of these. Also, many medications prescribed for mental illnesses (particularly ones for anxiety) are addictive so people may fake illness to try to procure drugs. But people also fake physical illness to try and procure pain medication - there is not much difference.
Which answeres the next question - yes, mental illness can be faked, at least to the general public. Hopefully not to a professional. But people who suffer from Munchhausen's (not by proxy - the one where they make other's sick, but when they make themselves sick) can fool doctors for years, so a person faking mental illness might be able to as well. Thst is sad, because so many people with true mental illnes
already don't have people believing them.
Depending on the severity of the disease, institutionalization might be the only recourse, for the safety of the patient and others. Only a doctor can decide if medication is best for a mentally ill patient. It is a case-by-case basis. Just like poeple with daibetes. Some can control their (generally Type 2) diabetes by closely monitoring their diet and exercise, while other need oral insulin, and yet others must have injectable insulin. The same goes for mental illness. A person with paraniod schizophrenia is almost always going to have to be on medication, it is dangerous for them not to be. A person with Clinical Depression can completely vary as to how much and what type of medication they take. Many people with ADD (which is technically considered a mental illness) find they can cope without medication at all.
From my personal experience as a Christian woman with Clinical Depression and Bi-Polar, the 2 do not have much to do with each other at all - other than the fact that they are both part of my life.
My son has Asperger's and is a Christian. He gave his life to the Lord 4 years ago, but there are many parts of his life that he has no control over due to his disorder. There are many that would question his salvation. I do not doubt his sincerity in his faith, but he has a very strong OCD component and very little impulse control. It is part of his illness that he is working to control and he takes medications to help with. As his parents we also realize that we need to help him with this be making sure he is not put into situations where he is in danger - or others might be. God will judge him one day on his actions but also on his disability. He will also judge him on what he has done to atone for what he has done wrong and what he has done to try and change it.
OK - this went way overboard, sorry, but this question is not a simple one. It is definitely a "it depends on the situation" type answer. And, abviously it is a little personal for me.