First, I'm struggling with understanding the difference between demens and insanum.
My understanding is that demens is an adjective (insane). I've also seen insanum in a few online dictionaries (here's an example), but I'm not certain it's even a real word.
Second, I'm trying to find a single word (a noun) for insane person (if there is even such a thing), but I'm not sure whether it's insanis or insanus because they both, once again, appear to be adjectives.
P.S. Now that it's been pointed out to me that there is, in fact, no such word as inasnum (it's insanus), I would still like to know the difference between it and demens.