The Hammers were 2-1 ahead before Kaoru Mitoma (89') and Carlos Baleba (92') turned the game around for Brighton as they won 3-2.
Potter lamented afterwards: "Unfortunately, the game is not 85 minutes.
"The game is 95 minutes or 100 minutes and so, yeah, I can talk about the positives, but I can assure you I don’t feel anything positive at the moment because the feeling is incredibly tough and the players can feel it as well.
"(They and we as staff are) devastated in the dressing room and they’re finding it hard to understand because they did a lot well.
"But we’re in the middle of a bad season where lots of things have gone wrong. There are lots of things have gone against us and not been quite good enough. And sometimes when you’re in those moments, everything that can go wrong, does go wrong, so it’s a cruel one for us.
"There were two (Brighton) goals from 30-plus metres, and it doesn’t happen very often (but) we have to look at ourselves.
"We switched off at the last corner and they’re able to take a corner and then you’ve got a player of Baleba’s quality from that distance and you leave yourself vulnerable to it.
"So, there’s always things we can do better."
"We're feeling the pain"
West Ham now haven't won in the last seven Premier League games and Potter admits the players are struggling.
He continued: "(We are preparing the team, working hard, but losing). That’s football – that’s the beauty of football and it’s the pain of football.
"We’re certainly feeling the pain at the moment. In the end, we all have to do better – myself, the players, we have to try to fight all the way to the end to get the points.
"There’s no lack of effort from the lads. There isn’t. Whether they’re able to sustain it for the 95-plus minutes, whatever it is, that’s another question.
"There’s a difference between feeling positive and acknowledging the positives.
"I absolutely acknowledge the positives because the performance was in large part really good.
"But it’s hard for me to stand here and take comfort from that at the moment because it’s painful."