I'm not saying there is no possibility, but it is my conviction that the experiences of a spirit realm to date more closely resemble the exploration of the interior of the mind than of some exterior world of spiritual beings. That said, this by no means degrades their meaning, if anything it infuses them with deeper meaning. For these realms exist within are, and are part of us, and can be discovered and explored. Within my own spirituality, the concept of exploring spiritual worlds, especially through the aid of entheogens, is rich and central, so by no means do I intend to suggest that these planes are somehow unreal or faked. It is just that their nature is not as it might initially be supposed.
Here's my theory for how they do it: you must first really, really want to believe it, cast aside your logical reasoning, meditate, do drugs, have a weird dream, or whatever, then mentally distort that totally ordinary experience until you believe you have reached the spirit realm.