The body is often referred to by some as a "Temple". If it is a Temple, then to be awake is like standing outside of same during the day and to have a dream is like entering the foyer of it by night...
Literally speaking, one does not take the body that they are lying in bed with into the dream just as they do not bring back, into this plane, the body that they were using to navigate throughout the dream, yet a person will claim ownership of both in the reports that are given by them.
However, the answer to the question that is the title of this inquiry that is often given is "Nowhere". The chair that I sit upon within a dream not only is not made out of anything but does not have a coordinate or place for it to stand. When I ask for evidence of this conclusion, there is none that can be given by definition. No particle nor destination thereof that one could point at or to. Yet the brain activity that is being measured and taxonomized suggests otherwise. If I take the conclusion as true then it means that the brain is able to facilitate the emergence and experience of "something" that is not made out of anything at all and thus why it is said to be absent. This does not seem logically coherent.
For example, hypnagogic jerks that occur when a person has a moment in a dream where they slip and fall down a set of stairs demonstrate that the body is reacting to something. If dreams are material/physical in some way, then this would be of no surprise as one thing that is physical will surely affect another thing that is. If they are not, then it becomes more difficult to explain. Not only do we have memories of things that physically exist but also of phenomena that does not physically exist. So, the definition of "existence" here includes all things physical alongside those things that are not.
Given the premise, dreams then can be taken as evidence of what is referred to as the "Transmigration of the Soul". Neither of the planes in question that a person can inhabit and have an experience of seem to be reducible to the brain but extend beyond it.
With all of this in mind, this can be taken as food for thought for the person who is told that their dreams "do not matter". What do you think? Do they or do they not? Is it worth ruminating about?