The problem is that the King James translators were quite loose with their use of "hell" and "hades." I've wondered over the years if they saw these two words as synonyms while we understand them to be two different places. Unfortunately, the New King James hasn't straighten out the confusion.
The New American Standard is more consistent in its translation: "If I ascend to heaven, You are there; If I make my bed in Sheol, behold, You are there" (Psalms 139:8). The realm of the dead, sheol in the Hebrew and hades in the Greek, is a place where God's presence still abides.
One thing you should keep in mind is that God is described as light. "This is the message which we have heard from Him and declare to you, that God is light and in Him is no darkness at all" (I John 1:5). But hell is described as a place of darkness. "These are spots in your love feasts, while they feast with you without fear, serving only themselves. They are clouds without water, carried about by the winds; late autumn trees without fruit, twice dead, pulled up by the roots; raging waves of the sea, foaming up their own shame; wandering stars for whom is reserved the blackness of darkness forever" (Jude 13). Darkness is the absence of light. Hell is a place God made where even His presence will not be felt.
As the Psalmist points out, we have never been away from the presence of God. It has always been there. Even death doesn't separate us from God. But one of the awful facts about hell is that God won't be there. You will not be able to pray and ask for deliverance because there will not be anyone there to hear you.
Take a look at "What is Hell Like?" for more details.

