Thanks for that question, this is typical example of a sentence where one has to think twice on what may have been the context and how to best answer your question.
First: the loosening of the etheric from the physical body is an important evolutionary trend that is happening right now and will continue in the centuries to come, it is important to study and understand this, because to it are linked the awakening of a new clairvoyance, christ in the etheric, .. but also it represents the first step in the pathway of spiritualization of mankind. As sketched in the Book of Revelation (and on the wiki site) .. through stages of ao the Future Oriphiel age and especially the next sixth cultural age .. in the sixth epoch will have the opportunity to spiritualize and disconnect from the physical body, the reverse of what happened in the third Lemurian epoch. A certain cohort will in fact succeed in doing so. A large group will not. In our times, the fifth and sixth cultural ages are key in this development, and RS tries to awaken people, just as John the Baptist did, to the fact they have to wake up to what is happening and change their ways so as to jump on that train of evolutionary development. He also mentions only a third of the population reaches a certain goal in any period, a simple statement worth pondering over.
Now in that context we consider the 'elemental unbalance' of Man's bodily principles, RS calls it the luciferic and ahrimanic influences mostly, but there are also the soratic (see also The double, on the page I think I add a simple introduction by Daskalos). Now I use the term elemental unbalance because this is Bardon's IIH way of putting it, the step 1&2 soul mirrors are the way of introspection and shadow work that is key in this. What Rudolf Steiner describes, e.g. in the 1917-01-GA174 lectures, is that the development of the I, in its long process, can go as intended, but most obviously also can go wrong at every stage of development of the I: imagine each cultural age since the Atlantean epoch into the current. So there is the model-blueprint or 'correct' I, but there also many illnesses or aberrations. The population consists of all these variants. And so if one is under the spell of a dominant luciferic or ahrimanic, that has all kinds of weird by-effects.
So: The ahrimanic clairvoyance you mention is a term never used by RS, because it is not clairvoyance, it is a form of delusion that may feel the same as connecting with the spiritual world as in well-developed clairvoyance, but it's actually the consequence of elemental unbalances or deformations of the soul that cause one to get visions, hear voices, etc. That is also why RS explains large groups of people will suffer from this in the future in ever larger degrees: nervous diseases and suicides will become epidemic. The materialistic culture will react by trying to 'protect' people (from these natural effects of spiritualization and the loosening of the etheric) by medical treatments (...). Some people believe this is what has started now, that by getting into a person's blood, the human esoteric physiology can be so affected as to shunt, delay or stop a natural spiritualization. But that's a different topic.
If you're interested I would suggest to read up the relevant sections on:
Human etheric body (for the loosening)
Stages of clairvoyance (eg the 1910-GA120 quotes on there relate to your question, quite literally)
Development of the I#Other (first bullet, and FMC00.338, and the related topic of the sixteen paths of perdition in Schema FMC00.233, more on those on Human races#Note .5B1.5D - The sixteen paths of perdition which also includes a 1917-01-GA174 quote)
Last, in the above it's important to realize that the origin of illness comes 'into' Man through the I and the double. You will be able to find richer context on all that I answered on those pages, including literal quotes from Rudolf Steiner's lectures, often with direct links.
Please let me know if this helped or not really, feedback and suggestions warmly welcomed.