Yes, this does sound very familiar to me. This is what would happen to me when I would switch, but before I ever started to lose time.
My system was designed to hide, like a lot of systems were. Mine could not afford to call any attention to itself, and that included switching. So, to not have me freaking out about black-outs and to not have an obvious switch in front of anyone (like my family), what my alters did when a switch happened was simply put me in the "passenger seat". (I often think of my body like a car). The alter who was "out" would "drive" the body while I'd sit in the background, still being able to see, hear, and know everything that was going on, but I wasn't in control. I also didn't know who I was, either.
Before I started recognizing my alters as being more than voices, before they had names and even for some time after they had names, I had no idea what was going on. All I knew was that I "lost control" sometimes. I still felt like me, I still knew everything that was happening, but then suddenly I'd be left going "wait, did that really just happen? was that really me? I'm not like that... am I?". The most difference I'd feel is a surge of emotion or something. Like with Kat, I'd feel a surge of rage. With Rain, I'd feel a surge of calmness and clear thinking. With L.C., I'd feel a surge of apathy and nothing could faze me. But other than that, I still felt like me, but when I'd look back on the memory, I wouldn't recognize how I'd act, or talk, or what I'd do. Like when I first majorly stood up to my dad (it was really Kat standing up to him for me), I replayed what had happened in my mind afterwards and thought "I don't yell like that. I don't swear at my dad like that. I swore at my dad! I don't do that. Who was that person? Am I really like that?".
It took a bit for switches to progress. For the most part, I think I was left "up front" but in the background because it helped my alter pretend to be me, which helped them to hide. At first they'd use my voice and not much about them would change except facial expressions and how they'd interact with people and react to things/people. Later on, as switching progressed, how they would walk/stand changed as well, but they would still use my voice (except Kat, who would sometimes use her voice when fighting with my dad). This is when I started getting pushed further into the background for switches. I'd still be there, watching and knowing what was going on, but when I'd be back in control and would try to remember what just happened, all I could really remember was the emotion attached to the memory. Like when Kat would fight my dad, all I would remember clearly is that we fought and that I felt a surge of rage and anger. I couldn't really tell you what was said or done, all that stuff would be blurry/fuzzy, but I knew what was going on at the time it happened. (So, by now I was experiencing "emotional memory").
I don't know if that's what's happening with you or not, but it's an idea. Una+ could be on the right track too, with you experiencing extreme depersonalization with possible identity alteration. I would definitely look into that possibility. You could have depersonalization with DDNOS, which would make sense, because it could mean that your alters aren't fully separated, and so it'd be really hard to tell who was out and when and stuff. (But I'm not a therapist so take this with a grain of salt, I'm just listing ideas that might be good to look in to).
As far as "getting somewhere", I'm sure a lot of people here understand that feeling. (I know that since I'm not in therapy, I sure feel like I'm getting nowhere sometimes). The road might be long and tough, but it'll be worth it in the end. Sometimes, you might not feel like you're getting anywhere, but just like any traveler walking down a road, especially a tough one, you'll need to stop and rest at times. Just try to stay strong and remember that after you reach the end of this tough, thorn-filled road, you'll be walking on a nice, smooth, paved road where it's smooth sailing (except for the occasional speed bump, of course).
Is there any way you can discuss the hospital issue with your therapist? Maybe you can get a note or even ask your therapist to escort you to help you bypass the body searches and everything? Or is there any way you could have your therapist with you during the body search, and could it be done with a nurse of a gender you're most comfortable with and only one nurse?
I'm sorry things are so difficult for you right now. -hugs if wanted- I hope things get better soon, and that you feel better as well.