Almost all of the changes are four-dimensionally offset from your original body. Some people call it your soul outgrowing your body or some similar nonsense, but it is quite provably material, as your new appetite and seemingly enormous density will attest. That's the first sign.

The next thing that will happen is that these new parts will start reaching out for support from within our conventional three-dimensional world. There's a lot of individual variability from this point, but there are three key things to look for: expanded awareness, agoraphobia, and lethargy. The expanded awareness will initially be very easy to mistake for just detecting vibrations through the floor, but eventually you'll be able to feel almost anything which is "underneath" your higher-dimensional mass, with great precision. The agoraphobia and lethargy are rather badly misnamed, and are actually entirely physical sensations: having to "peel" your hider dimensional matter from nearby structures. The discomfort when leaving a structure you're heavily attached to is more or less unavoidable, but regularly moving around inside it can keep you flexible enough to avoid getting stuck in bed.

In some cases, other people will also experience symptoms at this phase—if people near you feel an inexplicable pressure or things crawling over them at this phase, that's you! Remember that these motions are completely subconscious and you should not feel guilty about them.

In the longer term, your awareness will likely extend to your entire house or even your entire apartment building. It can be hard to keep track of your meat original body at this point, but it's important to do so at least until after your true sinews higher-dimensional form can feast becomes self-sufficient in terms of nutrition. For most people this just means as soon as you stop getting hungry, but appetite is not actually a reliable indicator! Experts recommend waiting at least until you've first started to form new architecture before you fully neglect your husk. There are surgeries to remove it fully, of course, though plenty of girls prefer to retain their puppet for various reasons. It can potentially make normal human interactions easier, lure prey, or help in cases where one or more headmates still have an attachment to an insignificant form. Should you wish to keep it, you may want to learn how to operate it manually; human biology is fleeting, after all, and decades are nothing to you now. You're free.