Drop it and Run
I randomly sat down once for a chat with a medical grad student at a dorm dinner during my freshman year of college. There was really no reason for me to be talking to her other than the fact that she happened to be a friend of a friend of mine.
Over the course of our chat, I casually pointed out that I had this weird red line that ran all the way from this ingrown-hair-like bump on my wrist up into my shoulder, following my vein.
She dropped her cutlery and looked at me in shock. She abruptly told me to stop eating and get to the emergency room, as that line was a staph infection and it was heading for my heart.
The doctor at the ER said (as he stuck me with an IV) that had I waited another couple of hours, I definitely would be in very rough shape (or possibly not even alive). Story Credit: Reddit/barndin