One definition, let me know if yours varies siginficantly:

"an emotional state characterized by the inability to tolerate the perceived pain or suffering of another.”

It's proposed by some as an outgrowth/improved term for compassion fatigue.

I suffered from some of this as a mother and had to heal it in therapy by working through my trauma and increasing my emotional carrying capacity to help my high needs daughter more. The alarm bells of my daughter's distress in combination with my PTSD getting triggered and chronic insomnia sometimes overwhelmed me. I felt her pain so deeply I couldn't effectively always mitigate it.

My daughter just suffered from it was well this week: my MIL was in hospital and my dd got sick from the worry. I was at least able to be there for her now though and have the carrying capacity for both our distress to help her feel better faster.