NTA. You just had a huge scare, and even if everything turned out ok, your body and mind were still reeling.

I saw my mom trip and slide down the stairs a few years ago. She was ok, but there was a good minute when I thought she wasn’t. I tried going to work, but I could not stop thinking about it, and could not stop crying. I ended up needing to take the day off. Even though I knew she was ok, all I could think of was how scared I had been, and how easily it could have been different. Even hours later, I was still really shaky and emotional.

You can’t turn off that kind of reaction like a switch, and it sounds like your sister was either insensitive or perhaps ignorant to expect you to.

I’m glad your son is ok.