There is a term "empath" and it's used for those who can sense other people emotions, sometimes without consciously knowing what's going on.
This is not used in mainstream science or psychology, at least not yet. Which of course means that it hasn't been "proven" yet/ hasn't really been studied or there are no means by which it could be scientifically understood...yet.

I've been told I'm an empath and even did an online training to learn how to deal with this, to stay grounded and not get lost in other people's emotions.
I'm very sensitive and my mood changes a lot when I'm around people.

However I'm still reluctant related to all this empath stuff. I mean there is something there, for sure, but I also think that very often when I feel an emotion when with someone, that can be also my reaction to them based on my own issues/ conditioning.

Like when I feel hopelessness sitting next to a person it might be that I associate his appearance with a story that evokes that feeling of hopelessness.

But in the same time, it happens the other way around, like when I was standing in line in the pharmacy and felt relaxed and was not in a hurry at all, then some older ladies arrived and I started feeling impatient, started thinking why does this take so long, and I saw that the old lady behind me was actually impatient.
Now I don't know if this was about feeling her emotions,but it seemed so. Or I noticed her reaction first and then became impatient?

But sometimes I think I'm just very reactive, everything evokes some strong emotional reaction in me. That's not others emotions, that's mine.

It's so hard to understand this.
Some people can just accept stuff and I used to but my mind wants to understand it deeper.