Work with me.
Let's say that all dreams are forms of nightmare. And thank goodness for that!
Even the ones that are kind of wish-fulfillments. After the fact -- after waking -- the residue of what can never be, that perpetual fading of the sought-for presence becomes not a pleasant oneiric memory. Waking up to such an absence leaves us in the beautiful atmosphere of a soft lingering nightmare.
Then there are the dreams expressing a continuum of lostness. Existential mazes of confused experience. The horror is subdued, folded into sagging planes of perplexed emotion. That is so damn groovy.
But the full-on nightmares. Those are superb. What can be better than a night of spiritual wrack and ruin? An unseen demon pounding on the door of sudden panic. Inanimate objects coming to sentience and malevolence. Danger. Possible death (a different form of wish-fulfillment) driving the soul to extremis and a grimacing delight.
All of this stuff of the night and great despond! What would life be like without dark poolings of such beneficence? A gift of nightmares is a treasure bestowed from the vast storeroom of uncanny art and deep pathological élan.