​Plaxico Burress -- Casualty In Real Estate Crash ... Takes Huge Hit on Florida Mansion

Plaxico Burress just got ROCKED by the real estate market ... 'cause he just unloaded his Florida mansion for HALF of what he paid for it back in 2005, TMZ Sports has learned.

We know ... Plaxico originally bought the 6,872 square-foot mansion in Lighthouse Point, FL back in September 2005 for $3.995 ... but that was right before the bubble burst.

Since then, real estate values in the area have plummeted -- and Plax just sold the place for $2 mil.

Official documents obtained by TMZ Sports show Plax was able to get rid of the house as part of a short sale (where the bank accepts less money than what's owed on the mortgage).

Unclear why Plax decided to sell since the house in incredible ... with a full media screening room, incredible pool, marble everywhere and a 100-foot dock.