Empathy is one thing, but having this particular condition takes it to a whole new level. The Huffington Post explains those with mirror-touch synesthesia can literally feel the pain of others (whereas empathy allows you to imagine how someone else is feeling).
This condition is apparently more common than you might think – the source says about 2 in 100-people have it. It happens when the “visual and tactile senses get mixed up,” and patients feel like they’re feeling touched when they see someone else being touched. You could imagine how this would extend to seeing someone get hurt.