Mealamu has suffered from a heart condition, which the Instagram video strongly suggests is the reason for the incident earlier this year.
The video also shows Mealamu has been in and out of hospital for the last two years.
Mealamu was due to compete in the main event of the Fight for Life in 2022, before a routine medical check-up discovered a medical heart issue.
It was discovered he has Atrial Fibrillation, which causes an irregular heartbeat.
It appears that he had been on the road to recovery and was taking part in a group fitness session before he collapsed twice, his head colliding with the wall.
It is unclear exactly when the incident took place.
The clip has been viewed 22,000 times and has drawn comment from former All Blacks teammates Piri Weepu, Tana Umaga, Ma'a Nonu, Charles Piutau, Victor Vito and Sam Cane.
Former opposition players Bryan Habana of the Springboks and Wallaby Quade Cooper also commented on the video, all wishing Mealamu a speedy recovery.
Mealamu had an outstanding 15-year career in professional rugby and is generally regarded as one of the greatest players to represent the Blues and All Blacks.
He finished as a two-time World Cup winner, with his last test appearance coming in the 2015 final victory over the Wallabies.
In the 2016 New Year Honours, Mealamu was appointed a Member of the New Zealand Order of Merit for services to rugby.
