If a Great White would have to remind myself to breathe as first instinct would be to become one with the surroundings. Would be looking to be sure he had no friends above, below or behind me, back up slowly to buddy, get back to back and exit quietly stage left, skipping safety stop unless deep dive. Would be mentally praying shark was stuffed to gills already and that buddy didn't pass out from fright or suck tank dry in next 3 minutes requiring intervention. Upon surfacing would execute the walk on water boat entry. Other sharks I'd probably be trying to take a picture but never chasing them for fear they do a sudden about face.