coolant issue and diagnosis

I have a 2001 BMW 325xi. The coolant light would come on and off, indicating I needed to have the level topped off. After almost two weeks, I did so, and at the same time had scheduled maintenance done. Upon leaving the shop, just getting on the highway, the coolant light came on again, but this time continuously. I called back to the shop, but I could not get back in that day. The mechanic indicated it might be the sensor. I drove this way for a week until I could come back again. The engine temp. always remained normal. The mechanic then said the coolant was empty, but when they filled it they could find no leak. He said he suspected that the engine might be burning the coolant and thus the head gasket may have lost integrity. Question: could a leak in the head gasket suck the coolant out in just a few minutes of driving? could all the coolant have been consumed in a week? I have owned this car from day one and never had any overheating or a problem like this before. Any insights, suggestions or advice would be greatly appreciated. if the engine temp is normal, it aint likely that all the coolant disappeared. most likely it was just the coolant tank that was empty. so u probbly didnt lose as much as u think, otherwise it would of overheated.

going by what u said, id rule out the sensor, even if it was bad it wouldnt cause coolant loss. but common sense tells u that if your losing coolant, its going somewhere. that means its either leaking on the outside of the engine or on the inside.

a blown head gasket is a possibility. if i had your car in the shop, id do a cooling system pressure test, to rule out any small external leaks that might not other wise be obvios. if there aint no external leaks, id do a 'block test' to check for combustion gas in the coolant, if it fails that test, that means either a bad head gasket or a cracked/warped head.

one sign of a bad head or head gasket is white smoke coming out of the tail pipe. but if the leak is small enough, this might not show up. so u should ask your mechanic to do the above tests.