Brakes

It is possible that whomever did your tune up knocked a vacume line loose, pop the hood and look at the large round metal thing behind the brake resivoir, this is called the Power Booster, there should be a small plastic piece with a hose running to the engine, make sure that is connected properly you can also remove this plug from the power booster and try blowing / sucking, (clean it first) this is a one way valve that alows air to travel only from the booster to the engine so if you put the side from the booster in y our mouth you should be able to blow not suck, if that appears ok then put it back toether and start the engine listen for any whistling noises that sound like a tire leaking air, there are many vacum connections on an engine some suck some blow, a chilton may help you trace the problem a little easier, and yes you should be careful to drive it until fixed, just remember a downshift may help you slow in an emergency situation also make sure your ebrake works and you can gently apply that to stop in an emergency as well