You can certainly shock fish with a suddenly bright tank and while it isn't a good idea (to do on a regular basis), I don't know that fish have the same startle reflex (reaction) as humans.
I would expect those awake enough to swim quickly away and those still in more of a stupor to follow suit as soon as they could, or realize no threat, but I wouldn't expect to find them breathing heavily.
That is my opinion from observing fish for a number of years...and I could be incorrect
(but doubt it..lol)
My 2 cents...two thoughts...first, when fish are at rest they tend to breath at a more regular pace (slower then we usually see) that may look like they are breathing heavily as we are used to seeing them sail across the tank with their gills closed (or steadily open...) so it is less noticable to us. Do look to see how it compares to what you saw when you turned the lights on early.
The other thought is if you have a lot of algae in your tank, it lessens the amount of oxygen available to the fish at night, so they may have to breath heavier to compensate. If that is the case in your tank, you may want to increase the available oxygen with the addition of an air pump until the algae situation is rectified. Not saying that is the case here!
..and where have you been, haven't seen you here in a while!

Hope all else is well!!