No matter how many times you tell your rational brain that a shark doesn't really pose all that much of a risk, there's no stopping your limbic system from reacting. I'm surprised you can't hear the sound of my heart pounding against my ribcage in this video. The shark is a gray reef shark. And he was probably about 5' or 6' feet long.
This second shoal was much, much larger than the first I'd swam through. Even after snapping a bunch of photos, I still had time to switch to movie mode and film this!