I have a lot of trouble staying grounded these days, and my T doesn't help at all.
But...when I was in intense therapy with my insiders, getting to know each other, etc..., and we had the same issues, that therapist and a group I was in at the time, along with some reading I did, helped me learn to manage the in-between times a lot better.
Not sure if you are DID, or if you have open communication with your "parts," but the biggest thing that helped me was to stop fighting all the chaos (which was huge for me for awhile) and sort of "sit" with it. I would listen to what was going on and, if I couldn't actively communicate with anyone inside, I would at least take note of all I observed. What I noticed was that the more I paid attention, the more I learned. Also, things became less chaotic. They got quieter.
Best to you.