"They're seizures that have been going on a while.
"I'm seeing the right doctors and they are doing all the tests and have got me on medication."
Johns rang his brother Matthew, the former player who is now league's No. 1 TV host, to inform him of the collapse, according to the report.
"He said he was standing in line to get served and could feel it coming on," Matthew said.
"Next thing he can remember is waking up on the floor. He's had a few seizures in the last couple of years but his last one was probably 12 months ago.
"He seems to think it comes on at times when he's really tired."
Johns is a league immortal, who was a famously tough and brilliant halfback for the Newcastle Knights, NSW and Australia.
The Telegraph reported: "...head injuries sustained by contact sport players is one of the biggest issues in world sport.
"The NRL will introduce a brain bunker next year where experts will monitor players during games for signs of concussion.
"Johns was once renowned for his party boy image but has lived a healthy lifestyle in recent years."