I had a similar pants-shitting moment in Pensacola 2 years ago while swimming with my kids. I was about chest deep and my 2 boys (6 and 11 at the time) had on life jackets so they were just floating. About 10 yards behind us, a bonita comes flying out of the water parallel with the beach, hauling ass like something is chasing it. About 30 seconds later, I see another bonita doing the same thing but this time about 10 feet away and between us and the beach. Naturally at this point I know something is chasing it so I look to the direction the fish came from and I see a gray dorsal fin breach the water about 50 or so feet away. It is headed directly for us so all I see is a slender gray dorsal fin hauling ass at us. Naturally I start to freak the fuck out so I grab the kids by the life vests and start running the fastest in water I've ever run before. It gets about 20 feet away and it makes a 90 degree turn.
It was a fucking dolphin, lol
About 30 min later and we're still out there swimming and a guy kayaks out a bait for his surf rod out about 50 ft away down the beach from us. Keep in mind this is like second week of June so the beach was absolutely packed. Way too packed to be fishing anyway. About 10 minutes later, we see tons of people that were swimming around us start getting out of the water. Then I see where dude reeled in a small black tip, like 2-3 ft max. It was nice because we had the water all to our selves for quite a while after that.