Your manager, or HR, is not just "someone". They are well above you in the power hierarchy. That's where the fear comes from.
People, when dealing with someone from a power position, need to be extra careful with their words and attitude - well, only if they want to be fair and don't want to toy with the other's emotions. I don't know if it's relatable to you, but it's similar to how much force you can use, when playing with animals. You need to be more careful with a smaller dog, than a larger dog. Cats are even more delicate, yet, not as delicate as a hamster. And you have to be extra careful, with the tip of your finger, to properly pet a mouse.
Similarly, saying "That's not good. I needed that for yesterday" is not the same for every person. If it's coming from your coworker, then it's maybe an oh shit moment, or something that you say sorry for, and amend it, and that's that. Much less so when it comes from your immediate superior. Even worse if it's an important client. And maybe even worse if you're a junior on trial period.
Would you accept the answer "no" with no additional context or replies without feeling put off? Chat is asynchronous. Just ask your question. This isn't a phone call or a desk-side visit. The act of initiating a chat already contains the idea that you are asking the other person for an interaction. If they have time to chat, they will chat. If you need a response right away, then chat isn't the place to do it.
Surprised at all the comments agreeing with this article.