I had the same thing happen; Assuming the bed bracket has been screwed in to the
wall, then you may want to look at the load on the brackets; You may find that
when you sit on the couch there is a load on the bracket trying to pull the
screws out of the wall;
Hard to explain, but I extended the brackets down to the floor, so all the load
would be vertical and not horizontal; I used square tubing from Home Depot. I
also used larger/longer lag bolts (measure first so you don't go all the way
through) - so far it's held up.
Hope this helps