Just got back from this, have no prior knowledge of the IP but wanted to give my theory on what I saw. Just gonna put the whole thing in spoilers-

[I think what happens when people enter the shimmer is that they make their way into the lighthouse and get cloned then killed/become one with the shimmer / self sacrifice like we saw in the video. To me this accounts for the gap of not knowing what happened how and camp is set up etc, when you "wake up" you're not YOU anymore so you don't remember those early times in the shimmer. The skeleton in the pool with the overgrown flowers had the infinity/snake tattoo on her forearm, this immediately made me think it was the REAL natalie portman(lena). I believe that in terms of this being an alien invasion, the shimmer achieved its goal of successfully infiltrating human civilization. It attacks a planet by creating an area that is inviting, learns everything it can, and then sends clones out to take over the world without any form of attack. I think the aliens are incapable of harm, they are only capable of cloning and adapting - but they need food.]#spoiler