I've been diagnosed with DID, which is dissociation based. Dissociation occurs on a sort of spectrum, from daydreaming through to loosing all sense of time or reality. For me the most extreme example is that sometimes I "regain awareness" in unknown places with no idea how I got there or where there is - for example when I lived in Aberdeen I once found myself in Glasgow! I also get what professionals have called "dissoaictive flashbacks" where I lose all concept on now and feel that I am totally in the past, or where I can
see people from my past following me about... one of these people is dead, and so at first I was totally convinsed that it was a ghost, but have now been assured that it's dissociation related. I have also had times where for days at a time I have apparently not done anything, not functioned in any way, not even moved, but to me it's like that only lasted a few minuets, which is a confusing consept...
as for hiding it... well people normally have no idea what dissocaition is, so they just assume that a person is "spacey" (people have nicknamed me "space cadet"

) and a little unreliable (when you're late to things or don't turn up at all).
Holding down a job is the biggest difficulty and employers are not too sympathetic to the whole "disapearing thing" nor to you seemingly not paying attention to things. But in a way I'm lucky as when I "zone out" someone else usually zones in to take over, it does mean that any work I do can be very variable in qality though, and back at school (before I even knew what dissocaition was lol) teachers used to accuse me of cheating as my handwriting would vary and the quality of my work was all over the place.
I don't think of myself as "ill" though, to me it's an adaptation that I took on in order to survive, and now that it's no longer needed it is causing issues but it's just taking time to adapt to a safer world
I have limited experiance with things like depersonalision, I have experianced it but only in short bursts, I can't imagine having it for long periods of time...
I can understand how from an outside observer it could all look like psychosis though. Esspecially as psychosis is more well known (even among mental health professionals it seems) than dissociation and so people sort of jump to the psychosis conclusion.