Thomas Nagel popularized the question "What is it like to be a bat?". The idea was to show that there is something more than physical involved in consciousness. My question is related but a little different. We cannot relate to bat consciousness as it is a completely different animal and have sensory system that we probably lack. What about a completely "insane human consciousness"? Is it possible from the objective and subjective data to construct a description so that we can all relate and imagine what it is like to be insane?
It is probably a variety of extreme things, just not at the same time... There is not one way of being sane, much less a single way of being 'absolutely' insane. Like Anna Karenina's view of families, functional minds are all functional in the same way, at least compared to dysfunctional minds, which are much more singular in their dysfunctions.
I am going to go way off in left field here and suggest that this is one of the reasons why recreational drugs are a good thing, even alcohol, and especially LSD.
Even if you cannot actually occupy the mind of a severe depressive, or a mild psychotic, you can gain empathy for it by pushing your own chemical status toward theirs and extrapolating. (As @CortAmmon points out, there are reasons for not really joining them out there at the extreme, unless you are quite sure you are just visiting.)
Being very different from yourself, occasionally, should help you keep in mind those very different from yourself.
There is power in the DMT experience of earnestly addressing See Urchins and Machine Elves, and really feeling what it means to be absolutely sure of something and totally engrossed in it, with no sense of 'game'-ness while the 'real' you knows that you are just flat wrong. There is similar value in the nebulous love of everything and everyone to be had when 'candy flipping'. Or the creepy feeling of living death on mescaline.
There is understanding to be had even in alcohol. People don't understand why the depressed, especially the bipolar, do things that keep themselves that way, and why it is so much work to even identify those things. Well, alcohol is a mild depressant, why do people drink? The reasons are endless, and all those same reasons make sense of mild mood problems.
Here is a possibility: that it is in fact no different than to be sane.
For in Kants theory of mind we can distinguish the Intellect from the Intuition; and it is the Intuition which presents the Intellect with sense-experience.
If the Intuition plays false and presents the Intellect with a false picture of reality, the Intellect has no choice but to construct a new theory of reality.
For example in conventional reality a wolf cannot suddenly jump through the wall into my room; but say that I saw that in fact it does hold; that in fact a wolf did just this once, then in this unconventional reality I can rationally hold that such things do happen.