I used to have more trouble with this when I was younger (not that I'm old, of course) and less aware of how to detect the difference between my emotions and others' emotions. The issue I'm talking of is picking up other people's emotions and then having my mind chatter come up with reasons why I'm feeling that way. I was mixing up my own emotions and other people's. And my mind became quite good at finding reasons to be mad or depressed or whatever, when, really, there was no cause.
Over time, I became better at telling the difference between my emotions and the emotions I was picking up from other people because the imported emotions felt a little like an ill-fitting sweater. A little itchy and not shaped for the real me. Once I learned that, I could consciously identify the foreign invader and let it go.
The reason I'm bringing this up is that since I'm under a teensy bit of stress lately (Significant Other has had major surgery, I'm nursemaid as well as working full time and trying to keep on top of the chores), I've been less able to tell the difference between my emotions and S.O.'s. Dear S.O. is on some pretty powerful painkillers, which I think cause some major mood swings. Enter Nurse Empath. She unwittingly picks up those emotions, most prominently anger and frustration, and then her tired, overworked mind starts creating all sorts of reasons why she feels angry and frustrated. Then, S.O., who is angry and frustrated and in pain meets Nurse Empath, and the potential for really loud sessions of venting anger and frustrations can occur. Not that I'm speaking from experience or anything. No, nothing like that. This is all hypothetical. Really.
Meanwhile, back at the ranch, I think I'll pick up my pliers and baling wire and go mend some fences. Adios, pardner.