The shell-shocked Seagulls conceded twice inside three minutes at Kenilworth Road during a defeat that meant they have won just three of their last 16 Premier League games.
Brighton have also not scored a league goal since beating Tottenham 4-2 in December.
"We are eighth in the table," said De Zerbi. "I don't want to make any excuse because we have to play better, we have fight, we must fight. I can explain this day as a blackout. It can happen, a blackout.
"We knew before the game the style of Luton, we knew everything. We didn't play.
"I believe in my players. I said the secret of Brighton is not the coach, not the recruitment, not the former coaches. It's the quality of the people inside the dressing room.
"Today is more difficult to say it like this. But I think they are smart, they have great values. They can analyse this day and we can learn from this game, from this defeat."
Brighton remain in the hunt for the European places and are also into the FA Cup fifth round and the Europa League last 16.
The Luton loss was only Brighton's second defeat in their last 11 matches in all competitions.
"This defeat is very, very, very tough," added De Zerbi.
"Luton played an amazing game, one of the best games this season I think. But I'm sure we played the worst game in my time this season."
Brighton next host Crystal Palace on Saturday, with Roy Hodgson's side going into the game on the back of their 3-2 victory against Sheffield United on Tuesday night.
