I made myself calm down. Whatever it was, it could've been anything, could've been a 'cuda. Still, I hurried back to the boat. Sanity was waiting for me there. Research is good.
Fear is an strong emotion.
It's an instinct. Clear your head and look at the reality of the situation. Replace irrational fears with knowledge, and the realization that the ocean is not our natural habitat. To enter it we must regard ourseleves as guests and regard our hosts with respect. Respecting sharks, while necessary for the animal's survival, may not come easy for most people.