Martijn Idioms are some of the hardest things in a language to master. I was very proud when I used "running on vapours", only to then realise the correct form is "running on fumes".

Mark Dain "Running on empty" is valid too. I had some of this when I was trying to learn German (I had this sweet job offer that fell through the floor), some of the idioms on Duolingo didn't make sense (IIRC, they had a seperate course for it).