“Q: Can there be any connection between a dreamer and an entity in “Kama Loka”?
A: The dreamer of an entity in Kama Loka would probably bring upon himself a nightmare, or would run the risk of becoming “possessed” by the “spook” so attracted, if he happened to be a medium, or one who had made himself so passive during his waking hours that even his higher Self is now unable to protect him.
This is why the mediumistic state of passivity is so dangerous, and in time renders the Higher Self entirely helpless to aid or even warn the sleeping or entranced person.
Passivity paralyzes the connection between the lower and higher principles. It is very rare to find instances of mediums who, while remaining passive at will, for the purpose of communicating with some higher intelligence, some extraneous spirit (not disembodied), will yet preserve sufficiently their personal will so as not to break off all connection with the higher Self.
Q: Can a dreamer be “en rapport” with an entity in Devachan?
A: The only possible means of communicating with Devachanees is during sleep by a dream or vision, or in trance state. No Devachanee can descend into our plane; it is for us – or rather our inner Self – to ascend to his.
Q: What is the state of mind of a drunkard during sleep?
A: It is no real sleep, but a heavy stupor; no physical rest, but worse than sleeplessness, and kills the drunkard as quickly. During such stupor, as also during the waken drunken state, everything turns and whirls around in the brain, producing the imagination and fancy horrid and grotesque shapes in continual motion and convolutions.
Q: What is the cause of nightmare, and how is it that the dreams of persons suffering from advanced consumption are often pleasant?
A: The cause of the former is simply physiological. A nightmare arises from oppression and difficulty in breathing; and difficulty in breathing will always create still such a feeling of oppression and produce a sensation of impending calamity.
In the second case, dreams become pleasant because the consumptive grows daily severed from his material body, and more clairvoyant in proportion.
As death approaches, the body wastes away and ceases to be an impediment or barrier between the brain of the physical man and his Higher Self.”
H. P. Blavatsky
The Mark Of God: Understanding Your "I AM Presence" 