Danny Welbeck struck twice either side Milos Kerkez's effort just before halftime for the 2-1 win at Falmer stadium.
Slot said afterwards: "First half was an equal game. It was a big blow for us that one of our two strikers that we have available with Hugo (Ekitike) and Alex (Isak) was already not here and the other one has to go off after one or two minutes - that is usually not helpful, especially when you look at how well Hugo played Wednesday. The first half was equal and the second half, Brighton were the better team on the pitch.
On Ekitike's injury, he continued: "The players and the fans know that there is only eight games to go to qualify for the Champions League and every game you have to miss is something you are upset about.
"Him going off and not being able to help the team - it is just a bit of bad luck. It is not like he will be out for three months but it is bad enough that he wasn't able to continue. It was a blow for him and a blow for us."
On Liverpool's 10th defeat of the season, Slot stated: "It is clear that we have lost a lot of points after playing in Europe. I have tried to explain a lot of times already why this is but today we also have to give credit to Brighton. In the second half, they were the better team on the pitch.
"That is what I meant before the game. What I thought was, you won't need 24 points to qualify and hopefully I am right because we aren't able to get 24 points anymore. We kept trying, in the second half we were close but they were closer to score the third one than we were the second one. Unfortunately it wasn't enough after a week like this."
On the pressure to clinch Champions League qualification, Slot concluded: "There is always pressure at Liverpool. On me, on the players. That is completely normal.
"We have qualified for the quarter finals of the FA Cup and the Champions League but in the league we need to make sure that in the end, we qualify for the Champions League. As much as I dislike us losing here today, Brighton away has always been a difficult one and will always be a difficult one as long as they keep bringing in so many good players.
"But there are other games where we should have picked up more points, like last week against Tottenham. That is far more unacceptable than this. But even away at Brighton, a club like Liverpool should be able to get a result."