Each person is different. So, each case of mental illness is unique, since it is in someone's personality which is not the same as anybody else's.
And a personality has spiritual roots. So, yes a mental illness can be a spiritual trouble, at its roots.
So, if this is true, whose spirit would bring a problem to someone's spiritual mind?
Our Apostle Paul says there is >
"the spirit who now works in the sons of didobedience." (in Ephesians 2:2)
You can see for yourself if a mental illness has a person thinking and obeying how Jesus has us love.
I know for sure how my mental problems have included anti-love things. For one example, paranoia can have me caring only or mainly about my own self, and I can be cursing others with worry and suspicion instead of blessing wrong people and caring with hope and prayer for people who are a problem for me. Plus, how I imagine dealing with problem people can be contrary to how Jesus says to love, in His Sermon on the Mount.
But, then, what happens because of being spiritually with God, in one's mind?
"'You will keep him in perfect peace,
Whose mind is stayed on You,
Because he trusts in You.'"
(Isaiah 26:3)
Also, if we pray the way God's word says to pray >
"the peace of God, which surpasses all understanding, will guard your hearts and minds through Christ Jesus." (in Philippians 4:6-7)
So, clearly my mental trouble is anti-love . . . disobedient to how God's word says to love. So, I consider mental trouble to be because of Satan's spirit of disobedience. But God is almighty to easily get rid of anti-love things from me. But if I try what does not work . . . it will not work!