Villa lost 1-0 on Sunday in a blow to their top four hopes.
Luiz said: "We are disappointed because we lost the game. Three points, even one point is really important.
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"Brighton is an amazing team. They're build-up is so good. The importance is to keep your head up and move on to the next game.
"It's football, you can lose. The most important things is to put your head in the same direction. We go together.
"We need to focus on the Conference League and go there and score two goals and win the game."