Hey, Bacon!
I did quite a lot of flip-flopping. I've had kind of a reprieve from that as an image of "the new me" is kinda taking shape. I identify with, and get along with, ftm guys than mtf girls. I was assigned male at birth, and I always gravitated towards tomboys... so I've started calling me a tomboy even though that means striving to be a bit girlier.
My mom's a feminist hippie, so my concept of gender is "**** gender, people can do stuff." So, I was never ashamed to do "girl stuff." However, my dad was a Marine, and a very manly man, which I took to like a duck in water. I'm strong, fast, uncouth, mechanically inclined, and my happiest place in life is freefall or the closest thing I can get to it. And I never got along with boys. Always felt like an outsider.
I never paid attention to my clothes (or really, my skin until something hurt a lot) or hygiene... so about the strangest thing in the world to me is that I started to crossdress. Freaked my wife out, too! I opened up a couple of times, and got the closet door slammed on my fingers (figuratively). Thanks in part to my own discomfort and my desire not to trouble my wife, I spent about a year in denial. Well, with both of us in therapy, things started to get better. I had about two months of very strong day-to-day genderfluidity... that was really rough. Really really rough. On girl days, I'd be in the pits because I'd see this man looking at me in the mirror, I'd be wearing these grubby boy clothes. On boy days, I'd think about the friends I'd told, the pain I'd caused my wife... the mental image of myself dressed femme made me want to puke.
Once, it all went away. Boymode for over a month! "Whew, wasn't that an awkward chapter of my life! Really wish I hadn't told anybody..." Before you know, it was back to the rollercoaster, starting with a giant crash.
Then, I had an idea: I'd just kinda sneak out of the closet. I like my life, I like my job, so I don't want a "new me," I just want me to be me. Gradually, I've been introducing girlier stuff into my wardrobe. I've got a transition plan: low dose hormones for a while to see how it goes, zap the beard & moustache off... maybe ramp up the hormones if that goes okay. The wife's on board, too! With a plan, and having found a noun that seems to fit, I find myself forgetting about my gender. I'm not preoccupied with it all day. There's still some variability, but it's not a huge swing anymore.
So for me, genderfluidity was a result of having the rational part of my brain hardwired for a gender binary world despite having a nonbinary identity. Now that I've settled on picking and choosing from "both" genders as I please, the bucket's stopped sloshing. I used to be a bit masculine of center, now I'm a little femme of center.