They were probably asleep. The sudden change in lighting blinds them for a bit and freaks them out. It isn't unusual, but it's not great either. Can be stressful. Usually they get over it pretty quick.
Well a lot of the newer lcd lights have a ramp up feature where they slowly turn on over a definable period of time. That is what we mean by 'ramp up' or for evening 'ramp down'. The intensity changes over a period of time to emulate sunrise/sunset.
As others have mentioned it's probably just you waking them up and blinding them a bit for a little while. Its kinda like when people turn the bright lights on when your eyes are use to the dark.
I personally don't have lights that can ramp up so I just have timers on mine and I have them turning on a bit later in the morning. So then the light from outside fills the room a bit to get them in a little brighter environment before the tank lights come on.
My lights all come on between 9:30-10:30am so even in the winter when days are shorter the fish still get some daylight before the tank lights come on.