Is there a word (or short phrase) that describes the sinking feeling that one is forgetting something, but but doesn't know what the "something" is?

Is there a word (or short phrase) that describes the sinking feeling that one is forgetting something, but but doesn't know what the "something" is?

For example, I'm looking for a word that describes the following feeling: Leaving to go on holiday, and two hours into your journey you feel sure you have left something important at home but just can't think what it is.