I take issue with the idea that mirror neurons cause emotional or sensory transference. That isn't what the research says.
Like a lot of people, I'm squeamish about eyes. When I (force myself to) watch an eye operation on TV, I feel horror, revulsion. I squirm. I might whimper a bit. Some people are too horrified to watch, some are fascinated by the technical operation, some aren't interested. Nobody's literally feeling a scalpel cut into their own eye.
If I see something harrowing, shocking or fabulous happening to you, you will see the emotions reflected in my face, voice, stance and so on. I'm not faking: this is sympathy. I'm not a crier but some will cry at your sad experience. I will definitely laugh at your comic actions. These are responses, we aren't experiencing the same as you.
Mirror neurons are mimic neurons with a range of intricate, subtle functions that are still being discovered. They aren't magic. I can't experience your emotions, because what you feel is unique to you. I haven't got your brain, your biochemistry and body, all of your past experience and your personality. I've got my own, and my neurons reflect what I believe you're showing me. I'm not in your head.
People with psychopathy have mirror neurons - they can learn and mimic - but their brains lack most emotional connections, so that mirror function doesn't work although they can copy your expression and my response.
People with congenital analgesia lack nociceptor function, so they can't mirror pain. They can copy the expressions but, again, it's fake.
It may be that 'empaths' have disorganised emotional or pain connections, leading them to think your experience has transferred to them whereas they're really mirror-responding. As far as I know, there's no science on that.
The inside of your head's all yours, though! Nobody else is in there.