A boy suffered injuries, which are only usually seen on fighter jet pilots, while filming a YouTube stunt in a kids playground.
Tyler Broome, from Tuxford in Nottinghamshire, passed out after a group of young people used the back wheel of a moped to spin him around on a park roundabout at high speed.
The group had been trying to recreate a YouTube video entitled the 'Roundabout of Death'. However, Tyler passed out and his Mum, Dawn Hollingsworth, later took him to hospital after his eyes started to swell up and close.
Ms Hollingworth said doctors told her his injuries were usually seen in fighter pilots suffering the effects of g-force and she is now warning others not to copy the prank, which could have had "life-changing consequences" for Tyler.
Extreme g-force can cause a blood flow from the lower parts of the body to the head and is considered to be potentially dangerous, as it can damage eyes and even a stroke in some cases.
Tyler has now regained consciousness and is being treated at the Queen's Medical Centre in Nottingham, where doctors are still assessing the impact to his brain.