Final answer:
The mass in the scrotal area described as feeling like a 'bag of worms' that changes with the patient's position is indicative of a varicocele, a dilation of veins in the scrotum.
Step-by-step explanation:
The description of "a non-tender mass" in the scrotal area that feels like a "bag of worms", which collapses when the patient is supine and refills when upright, is consistent with a medical condition known as varicocele. Varicocele is characterized by an abnormal enlargement of the venous plexus in the scrotum. It is often described as feeling like a bag of worms due to the mass of dilated and tortuous veins. Testicular cancer and epididymitis are other conditions affecting the scrotum and testes, but the clinical presentation described by the patient is more indicative of varicocele than these other conditions.