Villa striker Ollie Watkins celebrated his birthday with a goal and an assist for Morgan Rogers, putting his side ahead after Simon Adingra's early opener for Brighton.
But Emery's men allowed Lamptey to level with just nine minutes left at Villa Park.
Villa's hopes of finishing in the top four for a second consecutive season are in danger of being extinguished well before the spring after the latest erratic display in an inconsistent season.
Ninth-placed Villa are six points adrift of the top four, while 10th-placed Brighton's winless run has reached seven games.
Emery remains upbeat about their chances after a year in which Villa returned to the Champions League in impressive style.
"We played a fantastic match. The first 20 minutes we started lower than we were planning and we conceded one goal. But we reacted and came back with 2-1," he said.
"I have to accept it but I am a little bit frustrated. The table is very tight but we are in the race for the second part of the season.
"We have to be proud of the year. We have to try to accept it and be happy with the results we had in 2024."
Lamptey to the rescue
The Seagulls took a 12th-minute lead with a goal that encapsulated Villa's sloppy form.
Ezri Konsa failed to deal with Lewis Dunk's long ball over the top and it fell to Adingra, who fired into the bottom corner.
Villa could have been two down before the half-hour as Emiliano Martinez was forced into a full-stretch save to keep out Julio Enciso's shot before Jan Paul van Hecke put a free header wide from the resulting corner.
The hosts finally came to life and levelled after a frantic period which saw two VAR checks for penalties.
The first came after Rogers appeared to be chopped down by Van Hecke, but VAR official Stuart Attwell did not think there was enough evidence to overrule referee Craig Dawson's on-field decision.
From the corner there was more drama as Rogers was kicked by Joao Pedro after Seagulls goalkeeper Bart Verbruggen flapped.
Dawson initially did not award a spot-kick but eventually changed his mind after viewing the pitchside monitor.
Watkins stepped up to convert the spot-kick for his eighth goal of the season.
Villa needed just 72 seconds in the second half to go in front as Rogers grabbed his sixth goal of the campaign.
Watkins turned provider as his lofted pass from a recycled corner played in his England team-mate, who fired into the bottom corner.
But Villa couldn't press home their advantage and paid the price in the 81st minute.
Lamptey started the raid with a lung-bursting run before collecting Kaoru Mitoma's pass to fire home in emphatic style.
Watkins had two opportunities to win it but wasted both, leaving Emery holding his head in frustration after he lashed over in the final seconds.
