Irish Guards remain at attention after one guardsman faints in London, England, June 1966.Photograph by James P. Blair, National Geographic
I remember an ANZAC parade where the heat was getting the better of a lot of people, including myself. We were told to go down on one knee if we were feeling faint, which served two purposes - stopped you from smashing your face in to the ground from your full height, and allowed blood to rush back to your head. It also allowed medics to come attend if necessary.
The trick though was to eat right, drink right, and wiggle your toes and clench-then-relax leg and core muscles continuously.
That ANZAC parade was interesting for another reason too. One of the guys using a SLR with a bayonet mounted skewered his hand when doing a right dress. He said, “Ouch” but continued to stand at attention until a medic took him off the parade ground.
I was going to say that you wouldn’t want to faint and face-plant or otherwise skewer yourself on your bayonet on the way down. :/