The omnipresence of God is a reality (that God is everywhere all the time). “Where can I go from Thy Spirit?” David said (Psalm 139). And, since the coming of Christ and Pentecost, which was the sending of His indwelling Spirit to all who believe, the true follower of Christ is assured that Christ will never leave them nor forsake them personally. Once the Spirit comes to reside in the believing heart, He is there permanently.
But, it is possible to have our head turned by the world, the flesh, and the devil. We can quench and grieve the Spirit who lives within us. We can ignore Him or resist His leadership. If we do so, we will lose the conscious awareness of His presence. We will begin to operate on our own, not walking by the Spirit, and the results are always disastrous. We get what our humanity brings. Like an unseen guest standing in the shadows, He is still present, but not prominent.