Suzuki: brakes, vacuum booster, hydraulic brakes

Question
Suzuki Vitara 10 years old after coming of the motorway I pulled up at the junction to leave motorway I used my footbrake to stop , then went to pull away but the wheels had locked, and the footbrake I could not push down, I then switched the car off and after about 20 mins got back in and the brakes seemed to work,do you have any suggestion as to what it was.

Answer
It could be either the vacuum booster for the hydraulic brakes, or a mechanical issue causing the brakes to stay applied.
It can only be found and verified WHILE the malfunction is occurring.  There are NO electronic diagnoses of this possible.
You can replace all related parts, replace one and see what happens, or do nothing, hoping it won't re-occur.
My guess is the booster, but you must note that this is a SWAG (scientific wild-ass guess)