It was a problem with the Breathing Regulator/Anti-G (BRAG) valve supporting the Combat Edge vest, for F-22 pilots. F-16 pilots use almost the same vest, but the regulator and anti-G inflation valve setup is different.
The F-22 can sustain high Gs for longer which exacerbated the problem with the BRAG valve.
The F-22 can sustain high Gs for longer which exacerbated the problem with the BRAG valve.