Denis had undone his hat to salute the crowds when Night Train spooked during their victory lap after winning the La Baule Derby.
He landed on an ornamental wheelbarrow, broke two ribs, needed six stitches in his head and more in his elbow.
He told H&H: “I had taken my hat off for the lap of honour and was just putting it back on my head when he swerved and I fell.
“I shall certainly be keeping my helmet on in future.”
He said shows encourage winners to gallop around the arena in front of the crowd and, if you’re a male rider, you feel obliged to remove your hat.
But British team doctor Peter Whitehead said he felt the safety of such practices should be discussed by the industry.
“It’s obvious that flying around the arena one-handed with your hat removed puts you at considerable risk,” said Dr Whitehead. “Riders should keep their helmets on at all times.”
The rules of the international body for horse sport, the FEI, state that it is “compulsory for anyone jumping a horse to wear a properly fastened hard hat”.
And from 1 January 2013 it will be “compulsory to wear a properly fastened hat with a three-point retention harness at all times when mounted” anywhere on the showground.
But the rules add that senior athletes may be allowed to remove their headgear in prize-givings.
FEI showjumping director John Roche said: “Following the incident in La Baule the FEI jumping committee will review the ceremonial protocol.”
A spokesman for the Global Champions Tour said: “It is for each rider to decide whether they wear a hard hat or not for a lap of honour.”
This news story was first published in the current issue of H&H (24 May 2012)