James Vaughan equalised Leonardo Ulloa's opening goal but the Argentinian striker went on to claim a hat-trick, with David Lopez adding the fourth from the penalty spot.
Robins was convinced Ulloa's second goal should not have been allowed to stand, with the chance coming from a corner he was convinced should not been awarded in the first place.
"For 74 minutes I thought we'd get something from the game but it wasn't a corner and then we conceded," he said.
"We can't blame the referee but the second goal led to a capitulation.
"The two goals that followed came as a result of us thinking about the misfortune we suffered. Up to then Brighton hadn't hurt us very much.
"We had taken four points in our previous two games and we wanted another point or three, but it was unfortunate we conceded when we did."
The Terriers have won only three times in the league in 2013 and Robins recognised his side must bounce back from defeat as they are only five points above the Championship relegation zone.
"We've got a lot of work to do and not a lot of time left, we've only got two months," he added.
"For large spells of the game we did okay but we have to bounce back.
"We will certainly go forward. We have 11 games left and we're after as many points as possible. We also have some players coming back from injury and that will help us."
Robins believes his men must become mentally stronger if they are to avoid such defeats in the future.
"It's how you mentally put it behind you," he said. "We have to set up a team that suits us and, on this occasion, we stayed in the game pretty well up to Brighton's second goal."