((((((((((((((( Zorah )))))))))))))))))
I have dissociated to high degrees before with no evidence of another part of me stepping in. We're "good and well-versed" in that as well, I think.
Whatever the specifics are though, I agree with Petunia. Whether or not another part is stepping in, there's massive trigger, upset, overwhelm or something going on right now to cause this.
When I remember doing this, I was usually "running" fast and hard from feelings (no memories really). I was just running, running...emotionally and physically from adverse feelings that I "knew" would envelop me if I stopped.
Could it be that? If so, whew, this is tough... Historically I ran until it eased because I had no knowledge of what was going on, but once I did realize, I had to stop and sit...then usually some memory came along too.

I can't tell you what you should do if this is even the case because only you can suspect what you might be able to handle right now.
If you feel you need to continue to "run and do", just please keep yourself in safe situations until it relaxes some?
We're here and care.
KD