When you dream, you experience that as real, but then when you are back in your body it no longer seems real. Identically, when you die you experience various levels of existence that are as real as physicality. The problem is that when we are here in the physical body, our connection to the other levels is extremely weak or altogether gone, thus we do not "believe" they exist.

Stated from another angle, "heaven and hell" are relative to our state of consciousness. They are in fact real places that we experience just as we do the physical world, but we experience them in the bodies that correspond to those regions. (Just like when we dream).

So: heaven and hell are both: states of consciousness and real places. The two aspects are 100% linked. If your consciousness is conditioned by anger, lust, envy, etc, then your consciousness is in hell. You experience that here psychologically, and when you die, you will experience it more intensely.