For example , a microsleep episode is claimed to have been one factor contributing to the Waterfall train disaster in 2003 ; the driver had a heart attack and the guard who should have reacted to the train 's increasing speed is said by his defender to have microslept . For example , a microsleep episode is claimed to have been one factor contributing to the Waterfall train disaster in 2003 ; the driver had a heart attack and the guard who should have reacted to the train 's increasing speed is said by his defender to have microslept , thus causing him to be held unaccountable .