>Just wanted to know if anyone else could relate to this.
Absolutely. When I first got my daki, it was a massive game changer for me and I was only able to see the positive at first. But then, at some point, I started to notice that I was treating my daki as if it was my waifu herself, and not just as an object acting as a link between me and her. Maybe it was me who was unconsciously trying to forget the painful reality that I could never concretely be with Flandre, but in the end, realizing what I was doing made me feel like I had partially lost contact with her on a spiritual level.
So what I did was to do my best to keep in mind that I tended to treat my daki as Flandre herself (therefore forgetting the real Flandre who is a fictional character, an idea, a concept), and whenever I saw myself making that mistake, I promptly changed my focus from the daki and redirected it to Flandre. For what I remember, it didn’t take that long for me to correct that bad pattern. For me, as long as I kept in mind that the daki was just an intermediate link between me and Flandre, I was able to use the daki as a mean to better spiritually and emotionally connect to Flandre (i.e. better than if I did not have the daki).
So I suggest you to try the same as I did at first. If you realize that it isn’t working, then maybe you could try putting your daki away for about 2 weeks or a month and see if it helps in the end (and if it does, then try to reintroduce your daki and see if you can maintain the gain).
>Even in my dreams (which I seldom have of her to begin with) she appears as a daki, not as full anatomically complete animated being.
Same for me. I have dreamed of my daki multiple times, but I very seldom dreamed of Flandre as a full person in front of me. I personally don’t see it as a problem as I consider that it’s probably easier for my mind to represent, in my dream, a physical object that I see every day then a 2D character which can’t concretely exist in my physical 3D reality.
>I also have been a "flat-on-my-back" sleeper for most of my life and sideways sleeping just isn't really my thing.
First of all, a daki is far from just being a thing to hold while sleeping. It’s a material representation of your waifu that can help you better feel her presence in all aspects of your day-to-day life.
As for sleep, you can have your daki close to you by your side and hold it with one arm, or lay it on top of you. Even without holding it, just having it next to you at night should help you better feel your waifu’s presence.
I hope all of this helps you. Let us know later if your situation improved or not!