Everyone at my job suddenly hates me after I asked about a promotion

Just a month ago, I was getting tons of praise at my job. All of the managers were super happy with me, I was getting called in every week to come help out when they needed it because they knew they could depend on me. They asked me to help out with big projects, they always gave me great feedback and told me I was doing awesome.

Well, I mentioned to one of the managers that I was thinking of applying for a higher-paying position, and wanted her advice. She seemed sincere and gave me encouragement. However, ever since then I guess word has gotten around that I wanted to move up, and now all of a sudden, it feels like everyone has started acting differently towards me. All of a sudden, they stopped asking me to come help out with stuff and started scheduling me less. I feel that people have been trying to make me feel as though I'm not good enough for the position in subtle, passive ways (ex: they'll start talking about newer employees, that I helped train btw, that they think are great and should move up to that position in front of me.)

Yesterday, a coworker actually asked me to help cover for her because she wasn't feeling well. I agreed, and she called me back right after and told me that when she called to let them know I would be filling in for her, they told her that I, specifically me, could not cover for her because I'm a "slow worker", and that she either had to find somebody else or show up to work.

I was pretty taken aback because the particular manager who said this was asking me to come help her out literally all the time just a couple of weeks ago. nobody has ever spoken to me about my performance and told me I was ever going slow; in fact, when I'd ask they'd tell me the projects I was working on were looking "amazing." I sort of feel discriminated against now, hearing that ONLY I am not allowed to cover for somebody else.

It feels like the second I gained a bit of confidence and wanted to believe that I could do more were I given the chance in a new role, all of a sudden everybody wants to act as though I am a terrible worker when I was getting nothing but praise a few weeks ago. I don't understand why everyone's opinions have shifted so drastically; I know that I am good at what I do and I am not slow or incompetent in any way. I have thought about contacting HR because I don't feel as though I am being treated fairly anymore. Any advice or similar stories anyone has to share?

tl;dr: I asked about a promotion and now all the higher-ups at my job that used to be cool with me hate me and are telling my coworkers I'm not allowed to cover for them because I'm a slow worker.