It's most likely a "life flashing before his eyes" thing as he had his dome caved in by the kick.Why did BJ start hallucinating after stabbing the boss with the branch? did he get poisoned or did someone actually run between him and the boss and BJ twisted their neck? if he did get poisoned then when did he get poisoned?
I hope there's an actual explanation
I think BJ got domed in page 17 when the panel edges become wobbly.parts of this chapter felt confusing but I suppose the boss totalled his head the moment he got stabbed by the branch