I was driving normally, braked and all of the brake lights on my dash came on and stayed on. why?
If the brakes are still working, more than likely the brake fluid is low and has tripped the level sensor in the master cylinder. If so, more than likely your brakes are getting pretty skinny and might need replacing. What happens is, as the brake pads get used up, the pistons in the brake calipers extend, which allows more fluid to reside in them. The fluid level can get to the point where it trips the level sensor in the master cylinder. If this is what's happening, you don't want to just add brake fluid, but rather replace the brake pads. When the brakes are replaced, the piston is pushed back into the caliper, which pushes the brake fluid back into the reservoir. If you refill the reservoir and you then replace the brakes, the brake fluid will overflow the reservoir, creating a big mess.
Otherwise, if your brakes are not worn out and the fluid is low, you have a major issue. The brake system is a closed system, meaning you should not lose brake fluid unless there's a leak. If there's a leak, you DO NOT want to drive the car, as there's serious safety issues.