I've always found it frustrating that, by shoving a 'ness' on the end of a perfectly respectable adjective with an unproblematic meaning, a mysterious entity seems to have been born with properties that are taken to defy our understanding. We all know perfectly well what it is to be conscious. It's to be, well, not recently bashed over the head, to be able to respond to questions coherently, to have the capacity to draw on and lay down memories whilst engaging in complex actions, and all the rest of it. There are some rough edges to the concept which are exploited, as it were, by dissociative phenomena, sleepwalking, so-called blindsight, and the like. But on the whole we know what we are doing with it. Nominalise the adjective, however, and the temptation arises to suppose that one is suddenly in intimate possession of some quite marvellous and mysterious entity. All those Wittgensteinian lessons about such derivative nouns not gaining their meaning through an act of reference to a thing of some sort just go out the window.
Imagine if the same was true of the adjective 'tired'. We know what it is to be tired - it's, well, to be unlikely to be conscious for much longer. Stick a 'ness' on the end of it and suddenly we have this mysterious entity, this dying inner flame, called 'tiredness'. How will we ever fathom its hidden nature? How will we reconcile it with our otherwise respectably naturalistic worldview? This inner world of tiredness, this dimly evanescent internal force.... No! No-one feels compelled to even begin to wax mystical about tiredness. It is so obviously a noun which is the name of a fairly tractable property, a property the essence of which can be happily explicated through a list of what is true of someone if they are tired.
Similarly with happiness and sadness. In these long-post-vitalist days we are hardly likely to go round supposing that an analysis of happiness will be incomplete if we simply describe what is true of someone if they are happy - thinking that there is some mysterious stuff or property that these miss out - 'happiness itself'. But when it comes to more cognitive terms we immediately, or so it seems to me, start going off the rails. We forget to take 'belief' back to 'believe', and instead imagine that 'beliefs [who (setting aside for a moment political and religious uses) except a philosopher would use a plural of 'belief'?] are mental states' or some such, states apt for 'identification' with 'states of the brain' (whatever those are supposed to be). The active character of 'oh, i've got an idea, let's go down to the ...' gets lost, and we start to elaborate a philosophy of entity-like ideas, and even talk of 'mental representations'...
When it comes to the 'wondrous container' for all these states, ideas and experiences, the metaphorical nature of the 'mind as an inner realm' trope gets utterly forgotten. 'Conscious-ness' becomes a kind of final frontier for science. Yet, to me, (Lockean?) speculations about it are as likely to hold water as the commonplace speculations about the mysteries lurking in the depths of another famous Ness. Whilst the 'mysteries' cited in the 123,000 entries found by Google for mysteries of consciousness typically reference putative mysteries about the supposed referent of the term, the real mystery is why this mystifying hypostasisation still enjoys such philosophical currency.