Worf on the floor of the bridge after fainting.
Fainting was the sudden loss of consciousness often accompanied by a fall.
In 2268, half the crew of the USS Enterprise fainted due to the effects of the space amoeba. (TOS: "The Immunity Syndrome")
In 2269, Lieutenant Mira Romaine fainted while under the influence of the Zetarians. (TOS: "The Lights of Zetar")
Klingons generally didn't faint, except when ill. In 2365, after Worf had fainted on the bridge of the USS Enterprise-D, Doctor Katherine Pulaski described the cause of fainting as suffering a dramatic drop in blood pressure, blood glucose level dropping, and having deficient blood flow resulting from circulatory failure. Despite his protests, she checked the computer and diagnosed him with rop'ngor. (TNG: "Up The Long Ladder")
In 2366, the alien posing as Bolian Mitena Haro claimed to have fainted while studying before being abducted. (TNG: "Allegiance")
In 2370, Quark fainted upon learning that Pel was a female. (DS9: "Rules of Acquisition")
Later that year, Admiral Erik Pressman joked that William T. Riker looked as though he were about to faint when they came face to face. (TNG: "The Pegasus")
In 2372, Rom credited fainting with having saved his life, as it necessitated his visit to Deep Space 9's infirmary. (DS9: "Bar Association")
In 2377, Tom Paris thanked Seven of Nine and Icheb for assisting a pregnant B'Elanna Torres when she fainted. (VOY: "Lineage")