I pretty much talk about myself constantly here but I was kind of struck by this post so eh, you can feel free to ignore.
I was diagnosed with DDNOS which is basically a fancy way of saying "Very subtle DID". Of the DID people I have talked to it seems more controlled, more subtle, more switching at will, which is what I do. I am not really convinced that the dramatic sort of DID really exists, you know? That dramatic, completely unaware, complete fugue state, "United States of Tara" stuff. I don't think it happens, and of the people I have talked to they are very much aware of it. I don't have DID but I have been told I have something "like" it. I dissociate a lot, which I have always known. I lose time a lot, I lapse time a lot. I've been told it looks more like I am in a daze rather than going all insane and Sybil-y. I have even driven and done complicated tasks that I didn't recall. Scarily once I woke up in my car, I didn't know where I was going or where I was, I had no memory of getting in the car, etc. It was pretty frightening.
I switch between modes of "function" rather than personalities, at will, and each mode is an enlarged personification of a specific or useful attribute. Compartmentalization isn't really the main part of it, though I think there are some memories I don't have due to going extended periods of time in another mode, I mostly have all of my memories. For me it was more for the abilities I gained as a result, or the things I could endure as a result. There are good as well as bad, useful/non-useful for me. For example a useful one is emotionless and a non useful one would be regressed. Most people can't tell the difference unless they spend extended (as in years) amounts of time with me. I usually can't tell the difference either. Sometimes I can look back at my writing and point out all the switches, they mostly just look like changes in mood.
I was just diagnosed with this but I have known about it since I was a kid, I just didn't realize there was a name for it. It wasn't necessary voluntary for me (I remember as a child having the desire to "change" into something otherworldly or different and I remember voluntarily "ignoring" parts of my own mind and molding my own actions and personality traits, but the choice to do that wasn't really thought-out - I mean I was four and five and six, it was more reactionary) but neither is it something I absolutely cannot help. I reflect the situations around me usually, if I notice it I can stop it, etc. It definitely doesn't mean you are crazy. It doesn't mean you are hiding parts of yourself. It just means that you need to gain a bit more awareness of how you react to the situations around you, what you do with yourself, how you respond, what you think, are those thoughts different, etc.
For me I can identify some parts easier than others, for instance the emotionless part, because I will have more of a capacity to think things which have no empathy component. That is probably the easiest one, so obviously when I think things like that I can stop and kind of you know, recognize that is not a whole identity, or I wouldn't want to act based on just a perception or a persona or whichever. And obviously realize that I feel threatened at that point, which is usually the precursor to doing that. I think if you look at yourself and your behavior you will find you know a lot more about this than you expect you do, it's just that it sounds so "insane" as you say because it's not really, you know, the label is so intense, you think it couldn't possibly apply to you, but of course labels are just labels. Usually the label and the reality are very different.
This is actually the first time I have really talked about this in a lot of detail well more detail, a bit, just because I am pretty much going through the same process you are now. It sucks to be dealing with something so "intense", that it feels like you yourself are imagined or fractured in some way because it just doesn't line up correctly, but with everything I guess there is a spectrum. For me I find it kind of a private deal, like I really find it uncomfortable to talk about any "parts" you know as that, feels more personal to me, like my whole mind rejects the idea that people "know", not really because I am scared of being crazy (shit I am psychotic I know I'm nuts) but more my individual insaneparts don't like being put in the spotlight.
But I have met some people who are very comfortable with it and they seem to be able to have perfectly productive lives, just with a little added strange to the mix. I think there is something called integration therapy used to help treat it which means becoming more aware of what happens, of who you are as a person, of how your thinking or moods change, of what situations that happens, why it developed, in response to what situations, etc. I'm not sure what the end result is but it seems to be successful to some people.