Hello,first of all let me congratulate you for bringing this subject up!
DMT is a very interesting molecule,alongside with its chemical cousin 5-methoxy-dmt. More practical info about the experience of these two materials can be found at
http://www.erowid.org/chemicals/dmt/dmt.shtmland
http://www.erowid.org/chemicals/5meo_dmt/5.../5meo_dmt.shtmlAlso have a look at www.maps.org
Notice the similarity with serotonine....DMT is a quite potent endogenoys entheogen!!!
My personal take in the subject: The physical world exists and our logic and interpretation of reality works pretty well (it has allowed us to build working spacecrafts,build PC's even this forum! -this means that we have a pretty good ideas ,*applicable*, of our reality). Paraphrasing rhymer on his previous post ,our notion of "reality" is one that confers evolutionary advantage.For example ,if the filtering proccesses in our brain get shut down or downregulated 24/7 (which is a popular theory of how psychedelics/entheogens work),the feelings one would feel and the visual distortions one would see would be so disorienting that focusing on everyday survival tasks would be impossible. Now, under the influence of DMT one can experience non-ordinary states of consciousness that can be very helpfull and productive (given a safe enviroment) ,even reaching experiences and feelings of religious caliber!His /hers filters are down according to the theory and he /she can receieve information filtered out under normall circumstances Personally ,i wouldnt take it as far as saying about alternate dimensions,because i have no concrete evidence about their existence.Instead though of traversing the dimensions ,one becomes a psychonaut (like Argonauts,Homer) and can travel deep in his psyche/soul/mind.DMT can give you an experience that can transform your outlook on reality totaly.So ,in my humble opinion,its not a journey to parralel worlds its a journey to parralel states of consciousness...
As for the similarities of the experiences maybe they are archetypes.Images,behaviours and notions which are hardwired in our brains.Or they culd be redudant functions/"utilities" that our brain carries ,much like the appendix (from appendicitis,spelling?) found in you guts (some people argue that the notion of God is one of them)
I was quite lucky to have the epxerience and it was...well....humbling,powerful! Made me rethink of all the small things that trouble us in everyday life and about the nature of our consciousness...PLease exercise great caution if you are thinking of trying this neurotransmitter .(Because i dont know WHO is asking,and the legal side of the matter i cannot reccomend such an experience)
Any questions or comments are  highly welcome!
If you want me to elaborate on the pharmacology,philosophy or experience of this material dont hesitate to ask!