A 28-year-old woman presents to the emergency room with complaints of worsening fatigue and intermittent double vision. These symptoms have been progressively worsening over the last one month. She works as a teacher and the symptoms increase the longer she works on the black board, worse by the evening but relieved with rest. She has also noted drooping of her eyelids, which seems to worsen with prolonged working at the school. A detailed review of systems reveals some difficulty eating, change in voice quality, and weakness in chewing food. Physical examination discloses bilateral ptosis of both eyes that worsens when the patient is asked to actively keep her eyelids elevated. She has limb and trunk weakness in a proximal greater than distal distribution. Her symptoms markedly improved after edrophonium administration. Ice pack test turned out to be positive. Which of the following is the most significant emergency department complication of this disorder?