In the summer of 1788 the King's mental health deteriorated, possibly as the result of the hereditary disease porphyria. He was nonetheless able to discharge some of his duties and to declare Parliament from 25 September to 20 November. During the prorogation he became deranged, posing a threat to his own life, and when Parliament reconvened in November, the King could not deliver the customary speech from the throne during the State Opening of Parliament. Parliament found itself in an untenable position: according to long-established law it could not proceed to any business until the delivery of the King's Speech at a State Opening.