You have a dead water pump. Very common. Do NOT continue to drive the car. Have a new pump installed (or DIY). The pump itself is outrageously expensive, but you can cut a lot on the price by getting one online at getbmwparts or many of the sponsors of this forum. Have the thermostat replaced as well it is attached to the water pump so the work should be free.
Most of us have been there, don't panic, and do NOT drive the car further. You'll just increase the bill later down.