If your vehicle was truly "out of oil" it would turn a light on on the dash. You would also hear much more noise coming from the engine because is wasn't being lubricated.
Did you have this done at a dealership? If not, I would question them more on this. To lose that much oil in 6 months you would have most likely seen a puddle under your vehicle.
If they tell you that when they checked the dipstick they saw no oil, while that's a problem, there is still some oil in the pan.
Either way, you need to find out more about this if you can.
〉 Answered on Jan 7th, 2008 by Lori Johnson, Owner and Instructor at Ladies Start Your Engines