Historical source of the balancing exercises?

[Infinite]

Up to now, the only source I found similar teachings is justly the book "Initiation", quoted in session 41:

I forgot to write the author name. It's Elisabeth Haich. Here a stretch about a kind of balance exercise:

In these exercises, Mentuptah dictates to us various inter-related dream pictures which we must experience as intensively as if they were real. With these dream pictures we intentionally produce different emotional states within ourselves and learn how to control them. With these exercises Mentuptah takes us through all the different spheres of the underworld and overworld, through the seven Hells and the seven Heavens, teaching us to keep our presence of mind no matter what may happen so that even in the most difficult situations we can instantly decide what to do.

As soon as we have completely mastered this kind of exercise, we go a step further. We have to experience different emotional states on command, without dream pictures, but with the same intensity as if we really had a reason. We begin these exercises at the lowest negative condition, moving up step by step until we reach the highest positive condition. To take an example, we begin by experiencing the deepest state of dejection, moving up gradually through indifference, then on higher and higher, through joy and on up to the highest state of happiness.

When after long practice we get proficient at this exercise, we are obliged to practise faster changeovers from one emotional state to another until we can experience them all, one after the other, as easily and positively as a musician draws forth a whole gamut of tone from his instrument, from the lowest to the highest. When we achieve proficiency at running quickly through the whole scale of human emotions—from darkest desperation to the highest bliss—we take the next step. This consists of experiencing opposite emotional states, one after the other, with no time lost for transition, shifting from deep sadness immediately to the highest hilarity. Or, to take another example, from fear immediately to self-assured courage.

We are only permitted to do these exercises under the direction of our teacher. They represent a great strain for our nerves. It takes us a long time to reach the point of being able, with the aid of the dream pictures, to experience the emotional states as vividly as if they were external events in our lives. It takes us still longer to be able to experience the full scale of emotional states from the lowest to the highest. Only when we can bring our nerves to complete rest after these exercises, keeping them in a well-rested condition throughout the day, are we permitted to practise the most difficult exercises of experiencing diametrically opposite emotions without a time of transition. The aim of these exercises is to make us independent of both external events and our own personal moods, thus enabling us to determine our own moods ourselves and maintain our emotional equilibrium no matter what happens. We are taught constant inner watchfulness and presence of mind.

People believe that there always has to be a reason for their being joyous or happy. Through the exercises with the dream pictures we first imagine we have a reason for being in one mood or another. Thus we learn to control the reasons themselves! As we do not actually have a reason, however, we have to imagine one ourselves.

Then comes the next step of experiencing an emotional state by itself, without a reason, without having previously imagined a situation such as would call forth the mood to be experienced.

After long practice, when we have become quite skilful at these exercises, we discover we have always imagined we had a reason for being 'sad' or 'joyous', 'depressed' or 'exuberant' etc. Through these exercises we thus become convinced that events and occurrences in our lives must not have any effect on us. We discover that every state of consciousness arises—and can only arise—within ourselves. One and the same event can provoke one person to laughter, another to tears, while a third remains completely indifferent; all because each is merely projecting outwardly his own inward attitude, and it is only this inward attitude which provokes our response, not the external events themselves. As a final result, the pupil must attain the ability to keep his emotional composure imperturbable and unshakeable at all times, never losing it under any circumstances. These exercises also teach us that whatever happens on earth is only a transitory dream picture projected in time and space by ourselves. We only need to take it seriously in so far as it adds to our experience.