drop in (one's) tracks
1. To die suddenly. Brett always seemed so healthy—I'm shocked that he dropped in his tracks at 55.
2. To collapse, as from over-exertion. I hardly remember the end of the marathon because I dropped in my tracks as soon as I crossed the finish line.
drop in one's tracks
Collapse from weariness or illness; also, die suddenly. For example, I packed all day until I could have dropped in my tracks, or Grandfather's died; he just dropped in his tracks. The phrase in one's tracks has meant "where one is at the moment," and by extension, "instantly," since the early 1800s.