Sleep-related laryngospasm: This condition is characterized by sudden, brief episodes of laryngeal spasm that can occur during sleep, leading to expiratory stridor. It's often associated with sleep disorders, gastroesophageal reflux, or other irritants that can trigger laryngospasm.

Obstructive sleep apnea (OSA): While more commonly associated with inspiratory stridor, OSA can also cause expiratory stridor due to partial upper airway obstruction during sleep.
Laryngomalacia: A condition where the soft tissues of the larynx are floppy and can cause partial airway obstruction, leading to stridor. It's more common in infants but can persist into adulthood.
Gastroesophageal reflux disease (GERD): Stomach acid reflux can irritate the larynx and trigger expiratory stridor during sleep.

Epiglottitis: A life-threatening condition where the epiglottis becomes inflamed, potentially causing airway obstruction. Although less common, it's crucial to consider due to its high mortality rate if left untreated.
Foreign body aspiration: An object lodged in the airway can cause stridor and is a medical emergency requiring immediate attention.

Vocal cord paralysis: Unilateral or bilateral vocal cord paralysis can lead to stridor, although it's less likely to present solely during deep sleep.
Tracheomalacia: A rare condition where the tracheal walls are weak, leading to tracheal collapse and potential stridor.
Laryngeal tumors: Although rare, tumors of the larynx can cause expiratory stridor, especially if they obstruct the airway.