Originally Posted by James Withington
Whereabouts in the recovery do you blackout?
The intra-abdominal pressure caused from the Valsalva maneuver in heavy lifting can temporarily restrict blood flow to the brain. Try letting out a little of your breath near the top on the way up to relieve the pressure slightly. Obviously don't let out a large amount of air as you still need plenty of pressure in there, just let a little bit of air exhale while maintaining pressure.
I would say this is the answer.
I stimulated the valsava nerve, or whatever it is, when a fish oil pill sorta got stuck, or felt like it got stuck. I went down like a tree in the middle of our kitchen. Scared my wife and eldest daughter to death. Ended up with a nice concussion too.
Serious stuff that needs corrected if it can be done. There's a video of a young lifter doing a clean at a comp who once he recieves the weight and stands up with, simply falls over backward unconscious.
Good luck. I wish you the best in dealing with this as it's no easy issue.
All the best,