By the way, the sentences at the end of your article sound really strange :). Would someone really say them? I mean, in the meaning of "figuratively".
Could you just explain the coloured text, please?
Many people die of laughter. Figuratively. A much smaller number of people literally die laughing: unusual but not unheard of. But there is no record of anyone ever having literally laughed their heads off — that would have made headline news. (Although, on consideration, I suppose it might already have made headline news in the National Enquirer.)