Gastroesophageal Reflux Disease (GERD): This condition is a common cause of wheezing that worsens when lying down due to the reflux of stomach acid into the esophagus, which can irritate the airways and trigger wheezing.

Postnasal Drip: Allergies or a cold can cause postnasal drip, which may lead to wheezing when lying down as the mucus drips down the back of the throat and into the airways.
Vocal Cord Dysfunction: This condition can cause wheezing-like symptoms, especially when lying down, due to abnormal vocal cord movement.
Anxiety or Panic Disorder: Anxiety can cause or exacerbate wheezing, especially in the recumbent position, due to hyperventilation or other stress responses.

Aspirated Foreign Body: Although less common, an aspirated foreign body can cause sudden onset of wheezing, particularly if the object is lodged in a bronchus and shifts when the patient lies down.
Pulmonary Embolism: While less likely to cause wheezing only when lying down, a pulmonary embolism can present with a variety of respiratory symptoms, including wheezing, and is a critical diagnosis not to miss due to its high mortality rate.
Cardiac Causes (e.g., Cardiac Sarcoidosis): Although the question specifies no signs/symptoms of congestive heart failure (CHF), other cardiac conditions could potentially cause wheezing in the recumbent position and should not be overlooked.

Eosinophilic Esophagitis: This condition involves an allergic inflammatory response in the esophagus and can sometimes cause respiratory symptoms, including wheezing, especially if there is an association with GERD or if the inflammation affects the airways indirectly.
Tracheobronchomalacia: A rare condition characterized by weakness of the cartilage in the trachea and bronchi, which can lead to wheezing and other respiratory symptoms, potentially worsening in the recumbent position due to gravitational effects on the airway structures.