Not sure but I was under the impression they were 4D. I've heard many people say that 4D is where negative entities come from and 5D has many positive entities.

It would make sense they are slightly higher dimension than 3D because of how easy negative entities can influence or have an effect on us energetically. From a higher dimensional perspective it would be easier to see and interact with lower dimensional beings (us humans) and of course we can't normally see a 4D being because we can't see higher dimensions, we can however see 2D objects.

Personally I see it more like this: there is an astral afterlife existing side by side our real life, with many different planes or levels, and many different worlds or realms can be visited or lived in after death. There are places that have negative entities and places that have positive entities. Sometimes these beings interact with or manipulate our astral counterpart while we are still alive and have not yet crossed over to the great beyond. For them they would be existing in an earth-like astral reality that is very similar to our own. There could be numerous earth-based astral realms - both positive and negative. Normally our astral body is in rest mode whilst we are awake but when we sleep or die our astral body awakens. There are exceptions to this of course for instance meditation or pranic breathing, and varying levels as to how 'awake' your astral body is at any given time. Sometimes you can sleep and dream inside your own mental creation (which is based off your own personal astral realm) but other times when we sleep we can astral travel and not realise it, then there's intentional astral travel as well. I use the word astral but this is practically synonymous with the word energy or spirit.