[mann777]

what you are facing is loss of brake residual pressure when pressed. This has happened to me, I believe this happen due to change is external temprature, which may cause a locked up pressure to decrease in external temprature. This reduces holding level of the brakes.
One thing if you experience next time, get the vehicle parked by the side , ensure it a flat surface, put the parking brakes on, Ensure the Gear on "P".
Now pump the brake pedal to around 15-20 times, And release it. Wait for few seconds - Pump again for 5-10 times, Release it, One last time pump once ,ensure the foot brake pedal is depressed,completely, if the pedal has gone fully depressed and bottomed out , that means there is no pressure build up, Need to service you Master Brake Cylinder all four wheels and completely bleed the brake fluid out, Replace them with new one.
IF you foot brake pedal is depressed half way, and it has stalled, that means your master brake cylinder pressure build up is just fine. You are good to go. There is no trouble shooting further. let us know your outcome