So I've just learned that Anu has himself achieved Amaranth, and thus the world is in fact a dream conceived in his mind. Does that mean that Anu is the Godhead, or is he in turn a dream of the actual Godhead? And how does Padomay, as Anu's double, figure into his dream, if at all?

Anu is dreaming of himself and Padomay.

Anu is just one half of the Godhead, representing IS, with his brother Padomay being IS NOT.

Don't know where you learned that Anu is the Godhead, because I don't see it in any of the lore books that deal with Anu.

MK said Anu is/was Amaranth. Proof is in the A Children's Anuad

Here Anu fell asleep and began to Dream

This is within the dream.

Feel free to correct me if im wrong here, im certainly no expert in this area.

Anu was dreamed up by the Godhead. Later Anu became amaranth, and took over/'stole' the dream of the Godhead and reformed it. He didn't become the Godhead itself, because that is an individual entity. And like others have said above, Padomay is just part of that dream, and is serving as Anu's counterpart.

In my view, Anu took over the function of the Godhead, even if he's not called by that name. I think that's what you're asking, OP. I too was very confused when Anu's place as Amaranth was revealed, since I had previously asked if the Godhead was the Amaranth we were looking for (someone who had escaped a previous dream in order to dream up their own universe) and had been told "no."

Right, looked up the Annotated, and it starts with Anu and Padomay already present, which means that already, Anu cannot be the Godhead.

As we see, the two brothers just 'appeared'. There really isn't all that much, but from what I take it, it more about the two suddenly came to being when the Godhead's mind split in two, and the brothers, Anu and Padomay, were born.

For me, I see it less as him dreaming up everything, because Nir already created Creation, and instead went to to Aetherius and took a depression nap and didn't come back until Padomay returned after nursing his injuries from before.

Though, I personally do not find both Children's and Annotated to be literal, but a metaphorical view of the creation of the world so that mortals have an easier time understanding all the hubbub.

Makes me wonder if the Godhead's original dream really just seized to excist and was being replaced by Anu's version, or that Anu's dream excists parallel to the Godhead's. As in two parralel universes. If it has literally been replaced, what happened to the Godhead itself?

With how every interplay is pretty much the same thing, only on a smaller scale, I'd say the dream didn't go away, but went all Inception-like (the dream within a dream within a dream within a dream)

So did Padomay exist outside of Anu's dream originally, and then Anu dreamed him again in his dream, or is Padomay simply a figment of Anu's dream to begin with?

Both were originally present in the Godheads dream. As quotes from the anuad explain above.

And to note, Anu did wake up from his slumber when Padomay returned.

Here's how I think of it:

Godhead dreams of Anu and Padomay > Anu becomes Amaranth > Anu dreams of himself and Padomay, which eventually leads up to the Creation of Nirn.

But Anu awoke from his nap behind the sun, and there are there references that he dreampt, unless you imply that sleeping = dreaming. In addition, Creation was already created prior to his dreaming when Nir gave birth (and died right after). And after Anu woke up, he fought Padomay, but because both were too evenly matched, Anu threw himself and Padomay out of time (take this as you will).

This part of the myth makes me see things as such:

Anu was God in the beginning. His is God in the beginning because Nir professed her love for Anu, not Padomay. So, the original dream at this point remains. Padomay leaves in disgust, allowing Creation to be birthed by Nir and from Anu. Anu is still God at this point for all intents and purposes. Anu is hidden in the Sun and is dreaming that which is Creation...the original dream continues.

Padomay was jealous over Anu's creation (from Nir), returns to the original dream and shattered the 12 worlds. At this point the dream is "up for grabs." Anu "retook" the original dream by saving Creation, molding the shattered worlds into Nirn, and basically killing Padomay. Anu removes himself (and the remains of Padomay) from time, and the dream continues under His pretenses. Anu at this point becomes Amaranth. He does so because Padomay attempted to take the original dream and reshape it - Anu manages to ward of Padomay to keep his dream intact. It is through this concept of dream-stealing / dream maintaining that the concept of Amaranth is conceived.

I dunno...

As I see it:

The Godhead Dreams up Anu and Padomay. Anu and Padomay do their thing with Nir until Anu in depression goes to sleep and begins his own Dream. The Godhead's initial Dream continues: The Twelve Worlds of Creation are still hanging out in the Aurbis at this point, with Anu sleeping in the sun.

Anu Dreams that Padomay returns and smashes the Twelve Worlds of Creation. Anu Dreams that he wakes up to fight Padomay. Everything in the Anuad after this point is Anu's Dream, including Nirn as we know it. In the meantime, Anu is still sleeping in the sun. We have no idea what's going on in the Godhead's universe at this point, but assuming that nothing has changed (and we have no idea how much Time has passed, or if Time even exists in the Godhead's universe at this point), Padomay has left the universe entirely and the Twelve Worlds of Creation are floating around doing their thing still.

This is how I also see how it began, according to the Anuad.

This is where I disagree. I don't see it as Anu making a dream within a dream. I may be taking the story too literal, but I don't just see it (or that I think its malarkey), and that Anu really was just trying to nap off some depression and let time pass. And Padomay, like an overly jealous and resentful brother, tries to kill off Anu and Nir's children (12 creation worlds).

Though, personally, I find the Anuad is not a literal story, but another creation myth set in metaphor. Deals less with the details, and is more of the same two opposites fighting for the 3rd middle being. We see this story over and over with all the other creation myths, more or less, and that both Anuads is a romanticizing view of the interplay between the two polar opposites from the very beginning.