You're not crazy.  And it is not that unusual to see shadow beings in pairs or even a trio.  It's also not uncommon for some people to roll over and fall back asleep after an experience although this always surprises me. Either people really awaken, see the beings, figure they ARE dreaming and go back to sleep or the witness just assumes the beings are not harmful and too tired to give a damn.

I think one way shadow people appear to witnesses is when the witness is in a cycle of sleep that is deep but is slightly disconnected from the physical body in "astral form.  In the astral plane where this sleeping/astral form has shifted to, they can see other beings that exist on the same plane and some of these are shadow people.  It might depend on the level of consciousness one has at the time of astrally projecting into this plane that they can remember the experiences with shadows.  Many people wake up with the ability to see everything in their bedroom as it is, plus a shadow person but they find themselves still slightly in the astral, not completely grounded to the body. Some have the ability to move and react physically to the entities presence while others find their physical bodies paralyzed, unable to move.  Regardless of the physical state of the witness, they are seeing real entities.  Whether the experience is a pleasant, uninteresting or fearful one seems to vary from witness to witness.