For me these were the two most significant lucky situations.
* Caught a pumulary embolism low in my lung when the did my cancer CT test. Turns out I had a pe in other lung too. They were able to put in an ivc (inferior vena cava) filter before surgery to prevent a heart attack or stroke.
* While I was in a tcu (temporary care unit) I started feeling unwell. Had a nurse escorted me back to my private room and stay til I used restroom. I passed out and he got help immediately. I had an internal bleed and he saved me. I wasn't near a cord to pull, no roommate to call someone. Lucky he stayed.
How about you? Any "lucky" serendipities?