What is Sever's Disease (Calcaneal Apophysitis)?

Thank you ! No one explained this before

I’ve had this for 2 years and it’s still going

I had this over 20 years ago, in high school. Never knew what it was called. I hobbled around on crutches during the day in my junior year. After school ended, I'd put the crutches in my car and go play on the baseball team. Both heals were so sensitive. I was in pain for months. We didn't have internet back then. Had no clue what it was. But this video explains perfectly what I had.