That is what I call "Anchoring".

Taking an object, or interaction you are likely to pursue in the Astral planes and performing reality checks when encountering it.

I too find myself among endless crowds of people in my dreams, probably due to my occupation. Performing those reality checks, or elevating your state of awareness during that interaction is very effective, though difficult to execute as it will appear to the individual that you just had an absent seizure. Of course it is very important to execute your reality check with the up most enthusiasm and certainty. Remember, apparitions in the astral planes will look at you unusually like a regular person would, as they try to convince you that the plot of your dream is in fact reality.