This is the reflection on a realization that a thought is just a metaphor which is itself a metaphor, and so on. A thought about an object is not the same as the object that the thought is about.
It's recursive and maddening, a strange loop that provokes acceleration of thought.
Care in choosing metaphors can create a new mental structure that can upswing creativity, insight, or peaceful inner conflict resolution. This is made easier by the fact that the metaphor chosen doesn't have to be apt. In fact, sometimes choosing randomly is best. Then create a fit. The results may be bizarre.
It is a chest of drawers and each drawer holds many things, but if you open a drawer looking for a button there will be a button inside, and if there never was a button before it will be a button different from any other button. Perhaps pressing that button will make something interesting happen. And if looking in a drawer we find ouselves inside an artist making a sketch, and each drawer looks at each subject differently.
And so, with a vivid example of a randomly chosen metaphor being so modified, we turn to the effect of the process on the mind of the person performing the mental gymnastics. We will find that around several of the ideas that we ran across in the example a shortening of mental distance, an ability newly awakened to skip more quickly through frames of reference. The more this is practiced, the more speed and flexibility is gained, until a speed limit is introduced, usually by a fear of insanity.
The mind has now sped past the ability of the conscious mind to monitor and report on the coherence of its own thought.
Attempts at regulation at this point are considered largely futile, although the effects produced by the mind's attempts at control can vary over many degrees of instructiveness, and indeed cause many fairly spectacular instances of bizarre ideation, cognitive dissonance, etc.
Crucial to keep in mind at this point is that fear is the fuel of insanity, and it is fear that motivates the attempts to impose an illusion of control. Profound acceptance of lack of mental control may prove to be the wisest course here.
The slippage (again a metaphor, and one having to do with direct sensation) that occurs at the point of surrender to the sense that trying to impose control is worse than futile can be a very relaxing experience. This is akin to the relaxation a drowning victim feels in the last stages before death.
This last statement is a simile, which is similar to a metaphor, but is a comparison rather then an attempt to directly map ideas. Similes are fuzzy teddy bears. Metaphors are like rabid grizzly bears. One is nice to have to comfort you when you are young. The other can get out of hand and terrorize small indian villages before dropping dead in a pool of it's own saliva. On that point you will ponder.