My question is, can a Christian have a mental illness and still be saved? Can they have daily delusions similar to mine and still be saved?
Yes. But the life God calls us into in Christ is an "abundant life" (
Jn. 10:10), a life characterized by peace, joy, love, holiness, etc. (
Ga. 5:22, 23). Scripture tells us that the one in whom the Holy Spirit of God dwells has not been given a spirit of fear, but of power, and love, and a sound mind. (
2 Ti. 1:7) Over and over again the apostle Paul writes that peace and grace are found in a relationship with God. (
Ro. 1:7; 1 Cor. 1:3; Ga. 1:3; Eph. 1:2, etc.) What, then, of a life characterized by delusion, and fear, and psychological turmoil? How is such a life to be reconciled to the peaceful, stable, grace-filled life of the Christian believer described in Scripture?
I know that It's scriptural that once a Christian has salvation they cannot lose that salvation.
Yes. This is what Scripture clearly teaches.
I know for sure that I am born again, since I saw the whole thing.
And what if you hadn't? Would your second, spiritual birth be any less true? No. Be very careful, then, not to make your experience the basis of your confidence in your salvation. You are saved because God says He will save you in His word, not because you have had an experience that seems to validate God's promise of salvation. Your faith must not be in your experience but in what God has said.
But scripture also says in 3 of the gospels that if you commit blasphemy of the holy spirit than you have no forgiveness. Thinking that they Holy Spirit could be Satan could be along those lines.
What is at the very bottom of the Pharisees accusation that Christ cast out demons by the power of the devil? Why would they say such a thing in the first place? Were they speaking out of obsessive-compulsiveness, out of the addled thinking of a hyper-anxious mind? No. They had rejected Christ as the Messiah and sought to encourage others to do the same. And so they proclaimed Christ's power, the power of the Spirit of God, demonic. Doing so, though, was merely the result, a symptom, of their wicked heart's rejection of Christ. At the core of what they said was incorrigible, adamantine
unbelief and rebellion and it was these things that made them unforgivable, not saying, "The Holy Spirit is the devil."