I just wanted to note that MCTB-style insight meditation also draws quite heavily on the idea that we identify with muscle tension and that sometimes it feels like we're using muscle tension to make ourselves do stuff, or that our inner conflicts can be present in opposing muscle tension. The specific technique that you mention doing sounds kind of similar to a cross between Goenka-style body scanning and Tara Brach's RAIN technique (Recognize, Allow, Investigate, Non-Identification).
I'd encourage both you and the other rationalists who're digging into methods for breaking your sense of self into interacting sub-agents to really consider reading MCTB before you start continually applying these sorts of techniques to dissolve all your problems. Scott does a good job of highlighting Daniel Ingram's cautions about how many easy meditation techniques can seem to solve all your problems up until they completely stop helping and you end up stuck in difficult mental states:
If this last part sounds ominous, it probably should. If the fourth stage looks like a manic episode, the next five or six stages all look like some flavor of deep clinical depression. Ingram discusses several spiritual traditions and finds that they all warn of an uncanny valley halfway along the spiritual path; he himself adopts St. John’s phrase “Dark Night Of The Soul”. Once you have meditated enough to reach the A&P Event, you’re stuck in the (very unpleasant) Dark Night Of The Soul until you can meditate your way out of it, which could take months or years.
Ingram’s theory is that many people have had spiritual experiences without deliberately pursuing a spiritual practice – whether this be from everyday life, or prayer, or drugs, or even things you do in dreams. Some of these people accidentally cross the A&P Event, reach the Dark Night Of The Soul, and – not even knowing that the way out is through meditation – get stuck there for years, having nothing but a vague spiritual yearning and sense that something’s not right. He says that this is his own origin story – he got stuck in the Dark Night after having an A&P Event in a dream at age 15, was low-grade depressed for most of his life, and only recovered once he studied enough Buddhism to realize what had happened to him and how he could meditate his way out:
There's really nothing special about the existing meditation techniques that leads to this. Any consistently-applied enough introspection technique can lead there, especially if you're objectifying things as just thoughts, as sub-agents, or as muscle tension. I strongly suspect that the mental effects mentioned above are due to megadoses of the neurotransmitters underlying the Predictive Processing model. So I'd try to consider either limiting your use of methods like this or to acknowledge that heavy use might end up leading you to "meditate your way out" and read some discussions of what that might be like.
That makes sense to me -- both directing attention and looking at your sense of self often can feel like the ultimate Ugh Field. TMI does have some good guidance about building the skill of directed attention gently and consistently, but it's mostly in the early sections of the book and most people overlook it and tend towards exerting effort.
I haven't read it yet, but there's a new edition of MCTB that just came out with a lot of additional material. TMI is probably enough instructions to work from, but it doesn't provide as much meat around what you can expect to happen emotionally and phenomenologically.