Most deffinitely sounds like a bonk mixed in with some liver stress. Toxins from our modern, poluted lives are stored in our body fat due to most of them being fat soluable and will mostly sit there out of harms way. That's how our bodies work. Heavy exercise will induce our bodies to burn this fat and this is most likely what we want to do anyway however our poor liver has to deal with it and on top of everything else its not much fun.

Regards, Anthony