The most common cause of this being so sudden is the master cylinder. There normally is no warning other then maybe when stilling at a stop light or foot on the brake the pedal slowly drops. However, this is not a guarantee.
The best way to test this is to remove the outlet lines from the master cylinder and cap off the lines and then push the brake pedal (clearly make sure the vehicle is left in park because you will not have brakes). If it still goes to the floor then it is the master cylinder because the rest of the system has been removed.
https://www.2carpros.com/articles/brake-pedal-goes-to-the-floor
Let me know if you have questions. Thanks
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Sunday, March 29th, 2020 AT 3:09 PM