The miles to empty can actually go up while driving. I do mostly very local driving getting 12 - 14 mpg. If I get on the highway where I get better than 22, the number will stay the same for a while, then go up, then start going back down after a bit of driving.
My last 4 vehicles did the same thing.
If you need a shoulder to cry on ...
... pull over to the side of the road!