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Not just permanent damage. You can kill yourself holding in urine. The bladder bursts and the urine fries your innards. Fun.

FYI: You shouldn't drive with a full bladder. If you get into a car accident, it may burst and you'll be in all sorts of trouble.

Danish alchemist and astronomer Tycho Brahe died in 1601 due to complications from a burst bladder at a royal banquet in Prague, since he dared not leave the table to relieve himself as it was considered rude to get up when royalty was seated.