(And this is not in the way where spirituality and mental illness overlap. This is about making an analogy between "enlightenment" and being diagnosed with mental illness, even though these are different things.)
When you're diagnosed with mental illness, the world seems very strange, since you learn that what you thought was just your normal life was actually a mentally-ill illusion.
I remember being shocked when one day I was leading a normal life in high school, and a few days later I was "an anorexic" in a hospital, learning that the way I'd been living was really bad! I hadn't even really known it. It was a shock to me to realize that my normal way of life had been so blind.
Similarly, with spirituality, you might realize that what you've been doing almost all your life, thinking about yourself as an individual, has been an illusion, a sort of "mental illness."
It's really, really weird to realize that you've been seeing reality in a distorted, even grandiose or narcissistic way--whether by mental illness diagnosis, or by learning that it seems we are not in fact separate individuals.
Learning about spirituality might be kind of like realizing you've been paranoid schizophrenic, thinking that everything applied to you and was being done by you, when in fact it was just happening.
How weird!
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Credit: magic-and-spells.blogspot.com