A while ago, I posted some thoughts on Robert Monroe's out-of-body experiences. I remarked that many of his astral adventures had a dreamlike or nightmarish quality, and I wondered if maybe he was experirncing hypnagogic hallucinations.
That's still possible, but more recently I've become aware of the very large body of esoteric literature purporting to describe the stages of transition from this life to the next. One of the points consistently made by this literature is that the earliest stage of transition often involves immersion in a dreamlike environment. In this netherworld, the experiencer encounters beings and objects that are actually projections of his own mind - his hopes, beliefs, and fears. Adding to the confusion, the experiencer is typically in a trancelike state that impedes clear thinking.
Robert Crookall, who compiled many accounts of the afterlife from a variety of sources, maintained that it takes some time - usually about three days - for the deceased person to fully liberate himself from the remnants of his physical being. During this stage, the person's mind is clouded and his perceptions are unreliable.
I have not read the Tibetan Book of the Dead, but from what I understand, it warns against being deceived by exteriorized manifestations of one's own mind during initial postmortem experiences.
The topic is somewhat hard to address because different writers use different terminology. Terms like etheric body, astral shell, soul body, spiritual body, etc. are employed with a multiplicity of overlapping meanings. But the general point seems to be that when the physical body dies, the nonphysical body remains attached or connected to it for a time, and during this time there can be confusion and misperception. Part of the purpose of esoteric works like the Book of Dead was to caution people not to be taken in by these illusions.
Robert Monroe's more bizarre OBEs might best be understood this light. Similarly, the psychic predictions made by some near-death experiencers - which frequently fail to come true - may be seen as products of mental confusion rather than legitimate insights. We might also consider other dreamlike or phantasmagorical qualities of some NDEs as examples of this transitional state. When skeptics point to NDEs in which fantasy figures like Santa Claus make an appearance, one possible response is to observe that such encounters are fully consistent with thousands of years of esoteric teaching.