Did you remember to grunt?
During my attempt at the 'Recovery from the Vertical' exercise on the JP many many years ago when BEagle was a stude, I carried out the recovery iaw the instruction except that I continued to pull, through the horizon straight back to the vertical, whereupon my instructor took control. What happened? I'd blacked out pulling no more than 4G, why? Well there were probably a number of reasons, three of which were:
Heavy weekend
No breakfast
Didn't remember to grunt
Try grunting next time