Was the pedal hard and no brakes, or did it go to the floor.
If it was hard, the power brake booster works on vacuum and may have forze in the actuating valve (might of had condensation). When it warmed up, the moisture melted and voila!, you have power brakes again. Without the booster, the pedal is very hard and difficult to get any braking action.
You also may have had a frozen solenoid in the ABS. Same deal but brakes go to floor. Bleed your fluid to cure this.
