You are right. I'm pretty sure that's what happened.
The thing to highlight anyways is this: what, I think, made the shift was that. After the awesome sex, we both went to work 7am the other day, and pm us like 10am, to see if we got on time to work and so.. she said she was reaaally happy mentally, for having that sex and so. But then, was started to get cold and colder, that's when I asked her if everything was ok. cause we weren't talking as much as even before knowing each other, and it was weird, like something had happend, but until that momento, NOTHING had happend. So I started to get a bit insecure, and that's when I started with my questions of are you OK? And I started playing it like a more nice guy, etc... I hope i didn't messed it up completely and get another chance. Im too social with texts, sometimes I hate it.

As has been demonstrated time and time again, the "personality shift" signifies the low investment he has in himself.

From an attraction standpoint, women are far more interested in knowing where a man stands with himself and her - this is part of the attraction 'equation' in her determining her feelings towards him. If man has a low view of himself, he will have very little, if any, value to her. While it is true that one of biggest turn-ons for a woman is to feel DESIRED, it must be from a man who has a sense of purpose, and assuredness towards himself (not her). If he is lowly, meek, or displays any other attributes congruent with somebody that has a low self-opinion, there will be no fuel for her to feed her feelings of being desired.

You can't really feign being in your masculine either. For example, a guy labelled a douchebag or "creepy" in most instances she's aware at an intuitive level that he's not what he's selling himself as - she may initially feel desired somewhat, but soon after once she realizes its all a façade/a smoke-and-mirrors act, she'll move on.

post the chat log so we can see

Lol, as I said in my first post, I'm from Argentina. So I don't think It would make a lot of sense...
She also, when I asked about her weird vibe, sad that that day she had some tests results, that werent very good. So she was kinda low energy, but nothing with me. She seemed almost non interested in keep chating, that's why my needy alert came up. I didnt got to read her very well. So we chatted about some other stuff, movies, etc. I recommended her a movie, she said she'll watch it, etc. And I finished it with a "sounds good", literally in english, cause we speak it, as fun. 2 days since that, so im not chatting her again, im waiting for her to make a move. Otherwise maybe I'll chat her on sunday, cause monday is holliday here. If she says no on sunday also, im screwed and will feel like shit. Should I even ask her out again on that sunday? or should I let her invest now? I mean look for me. Cause maybe she espects I look for her again "like men are supposed to", you know.

Text her with definitive plans for the movie date. You're coming off as wishy washy, that's not attractive. This is what I am talking about when taking the lead.

What do you mean by wishy washy? not sure with the reference.

No Just no.

Don't check in like this without being in a relationship.

Argh.
You're fine. As long as you are self-aware, it's all good. And there is a fix:

Don't contact her.

You have to go through a Needy Cleanse. Be the bad boy who fucks her the first night and doesn't contact her for a week. This will reverse the needy damage you have done. I do this with every new woman I fuck (if I like her, that, is). Every guy who fucks a hot woman acts like you did here, and girls run away. I make myself stand out by applying this method every time.

When women get themselves off, they don't think about a nice, clean cut well behaved man bringing them flowers, or laying rose petals upon the bed. They think of eating out a hot girl's pussy, or getting banged by two guys, or sucking off a drug dealer for coke, or being thrown against a wall, all sorts of dirty scenarios. It's OKAY to be that guy. In fact, it's better to start.

Be congruent with your desires. You don't want to be "friends" and to make sure "she's okay". You want more sex.

_________________
Pickup coach. PM for direct, simple coaching.

Not clear, ambitious errrr indecisive even

TRUTH.

_________________
They call me the cat whisperer, cause I know exactly what the pussy needs.

Ok this was really helpful and true. Im glad I came here, needed a punch in the face with a chair.

I wont contact her. And I really need that needy cleanse.

Thanks a lot. I have to work on this.
Ill let you guys know of any update. Ill stay more focused.