It's just a term. You can as well say that he experienced "shift in perception (or awareness)". Expression "journey into a higher level of reality" is idiomatic for all religious misinterpretations of said phenomena--shaman or mystic would use something along the lines of "journey into a different world". The difference is subtle but substantial. Nevertheless, such terminology without proper context (exactly as terms like "hallucination" or "delusion" due to their modern connotations) is rather prone to all kinds of misunderstandings, because even though the latter perfectly denotes what's going on, it may evoke a notion of separated worlds (and even sorted according to some hierarchy as seen in the case of the former), whereas reality is but one, we just rarely perceive it that way. It's all a matter of understanding and interpretation. Well, if Saul was aware of the nature of his experience, he would not invent his nonsensical pharisaic messianism.