Nocturnal Enuresis (Bedwetting): This condition is characterized by the involuntary urination during sleep in individuals who are developmentally able to maintain urinary continence. It's a common issue in adolescents and young adults, especially if they have a history of bedwetting as children.

Polyuria: This refers to the production of an abnormally large volume of urine. It can be caused by various factors including diabetes insipidus, diabetes mellitus, or excessive fluid intake before bedtime, leading to nocturia (the need to urinate at least twice during the night).
Sleep Disorders: Certain sleep disorders, such as sleep apnea or restless leg syndrome, can increase the likelihood of nocturnal enuresis by disrupting normal sleep patterns and potentially increasing the pressure on the bladder.
Neurological Conditions: Early signs of neurological conditions like multiple sclerosis or a spinal cord injury could potentially lead to urinary incontinence, including nocturnal enuresis, though these would be less common in a previously continent 19-year-old without other symptoms.

Diabetes Insipidus: A condition characterized by the inability to regulate fluids in the body due to problems with the antidiuretic hormone (ADH). It leads to the production of large amounts of diluted urine, which can cause nocturnal enuresis. Missing this diagnosis could lead to severe dehydration and electrolyte imbalances if not properly managed.
Spinal Cord Injury or Tumor: Although rare, any condition affecting the spinal cord can lead to neurological disturbances, including bladder control issues. Early detection is crucial for effective management and prevention of further complications.
Epilepsy: Nocturnal seizures can sometimes manifest as urinary incontinence during sleep. It's critical to consider and rule out epilepsy, as untreated seizures can lead to significant morbidity.

Bladder Exstrophy or Other Congenital Anomalies: Though typically identified in infancy or early childhood, some mild forms of congenital anomalies might not be diagnosed until later in life, potentially causing urinary incontinence.
Autoimmune Disorders Affecting the Bladder: Conditions like interstitial cystitis can cause urinary frequency and incontinence but are less common in young adults without a history of urinary symptoms.
Psychological Disorders: Certain psychological conditions can manifest as urinary incontinence, though this would be rare and typically associated with other psychological symptoms.