Another royal who had Porphyria was Frederic the Great--and there are certainly blood ties between his line and the British royal line! You might want to read Nancy Mitford's biography of Frederic--it's the best one available of this particular monarch, and it does address this illness.

As for high tolerance, I do have a relatively high tolerance for pain meds, and many years ago I actually woke up during surgery! I can still vividly remember the consternation of the surgical team, and someone saying, "Get her back under, quick!"

Luckily, it's never given me nightmares over the years--just a few chuckles!