Hi cj,

Yes, over active bladder is a medical diagnosis.  You might have seen commercials for Detrol LA.  This is one drug given for OAB.  When researching medical conditions on the net, beware of .com sites.  Try .org sites instead.  You may find the same information; for instance, on www.urologyhealth.org as the site you researched.  However, many .com sites are not acknowledged by physicians like the .org sites.  This was found on the site for you:

What is Overactive Bladder?
Overactive bladder (OAB) is a condition characterized by a sudden, uncomfortable need to urinate with or without urine leakage usually with daytime and nighttime frequency.

OAB occurs when smooth muscle of the detrusor muscle of the bladder squeezes or contracts more often than normal and at inappropriate times. Instead of staying at rest as urine fills the bladder, the detrusor contracts while the bladder is filling with urine.

This condition is not usually associated with severe pain as you quoted from the Tom Hanks movie, but can be uncomfortable.  If you look up how it is diagnosed, they have done many tests on you already that should have given them a clue.  The cause of OAB is unknown, but urologists do have an idea of underlying conditions that contribute to the symptoms.  These underlying conditions as well as treatment are on the site above.

Hope this helps.