Long vs short switches

My longest alter has been out for 15 years (I guess, I don't know about the time before being 17).
*Trigger Warning*
It got abused as well and fragmentated.
Now she herself is dormant (or dead?), which is hard, because I don't know who "I" am.
I do not remember much of her being out, and do not posess her abilities, thus as she has disappeared I am completely lost, do not know why I life in the city I do live in (emotionally, not from reason that she has moved there), but have no attachment whatever to the live I am living (involves people I "know", city I live in, the work she did...everything). I am completely alienated.
She was forced to leave and she was always begging "not to make her leave".
Timeloss to me can also be that I am having a vague memory about what has happened (but really vague), but no emotional attachment at all.
edit to add: since she is gone (the dancer) I do have short switches daily and in some situations alters coming out for a couple days or weeks, but it is all blurry (cannot really remember time from January until July this year, just some events and it is all confusing).

I have lost 2 weeks before. Kinda scary first time it happened. Generally its a few hours. Occasionally a day or two. Definitely dependent on the time of day i switch.

I have trouble knowing when it is that an alter is out. Is it when they say things that you don't feel in your throat or think about, and you feel this odd sensation in the frontal lobe? Or can it also be going on when you aren't feeling any dissociation, but you are definitely changed? I know that I have a bunch of different personality setups that happen, and some have way more dissociation than others. My main personality has a lot of dissociation, but one of my alters has it so bad that I barely can feel anything at all.

I switch to one years old, whenever I get up and walk. It's like I descend down. I usually stay at one years old, because whenever I come out of that, I can't function. Around one years old I was hijacked by somebody, so I have to go back to one to survive.