The visitors were on terms within 60 seconds of the restart, midfielder Lansbury rising to level with a superb header from 8 yards following a corner from Majewski.
Keeper Darlow prevented** **Brighton from regaining the lead only 3 minutes later by pushing a goal-bound shot from Barnes onto the post.
Two goals in the space of two minutes put Forest firmly in charge with a strike from Henderson and a spot kick by Lansbury boosting the visitors.
Forest were reduced to 10 men on 67 minutes when Chalobah, booked earlier for a foul, received a second yellow for a push on LuaLua.
LuaLua had a curling free kick saved by Darlow as the Seagulls struggled to launch a late fightback.
More top news
Rain will arrive through the early hours for a wet start to Monday. It will eventually brighten up by the afternoon.
Rain on the way tonight, then a wet start to Monday, but it will brighten up through the day with sunny spells for the afternoon.
One of nine dogs dumped on the streets of Winchester, unable to see or stand properly, is fighting for its life.