I once heard a psychiatrist assert that consciousness is probably an illusion. He was an extreme example of being polarized toward the medical model of mental illness.
There are some psychiatrists and others who worship science and believe it is the whole answer to life. They don't realize that their dogmatic clinging to the belief that today's science must account for everything (or else it doesn't exist) is a religion too. It is arrogant to believe that human knowledge is anything but in its infancy.
The reader shouldn't construe that I am siding with creationists, who I believe to be deluded members of a Christian cult. I am simply saying that physical science isn't nearly advanced enough yet to justify the level of faith in it that some people have. A good scientist ought to agree with this.
Then you run into the New Age spiritual healers. Some of them do this as a business. Unfortunately, you have no way of knowing in advance that the healer knows what he or she is doing, understands your particular set of needs, and won't worsen your problems or create new problems in the process of what they are doing.
When I tried some new age healers and groups when in my twenties, I finally realized that I might have been letting go of some bad material, but my defenses were stripped, leaving me wide open to entirely new problems--I lacked the defenses necessary to deal with a sometimes challenging environment.
The good that I received from studying meditative works by popular New Age authors in the 1980's was that it taught me the folly of force, and it got me started with using cognitive techniques to help relieve pain. These are two important lessons that I am still learning.
Hope of something better, for someone with mental illness, should not be underestimated. Thus, when I was much younger and even today, the possibility that the future holds something better has been enough to keep me going. The idea that I could practice meditation to make my life better allowed me to persevere during my young adulthood--which was an extremely difficult period in my life.
Organized spirituality, for many persons with mental illness, can be a refuge and a source of hope. These two things are sorely needed if you have these illnesses, which create misery from the inside out.
For someone with mental illness who would like to feel better, I would recommend a class in cognitive therapy. It could be a class offered by a reputable source, perhaps one affiliated with Adult Education, or with a hospital.
Spiritual practices do not conflict with accepting treatment for a mental illness.
Groups like Scientology and the like are to be avoided. The mind's power can be harmed when misdirected by an external influence, including in the context of it supposedly being a healing.
If a church, synagogue, or mosque puts wind in your sails, then you are doing a good thing. Absolute atheism and worship of "modern" science (which seems to dispute the existence of a soul) does not offer much hope for a person with mental illness, since it labels persons with mental illness as little more than biologically defective machines.