As we live, our consciousness produces energy used to interact with, to monitor and control this body. When our body dies, our consciousness uses its energy to create a new ghost-like body.
Our consciousness doesn't have a location, and the location of energy it produces is decided by our state of mind; when said energy returns to the source, we experience sensations.
But our true core is not our consciousness, it's a thick strand of energy that forces us to continiously interact with one specific body. When all of this energy returns to the source, all traces of our mind are extinguished, and a new strand is formed and takes its place. This is how spirits die and are reborn.
As for dimensions… There is a set of strange locations that are based on, are attached to and influenced by this planet. It can be said to be in the 4th or 5th dimension. Other realms, I'd say are comletely separate from us.