lose track

To lose track is to stop being able to follow something you were following. You look up from the book and have no idea whether it is four o'clock or six.

It takes of, and almost nothing else: you lose track of time, of the score, of an old schoolfriend, of how many cups of coffee that was. Time is the commonest by a distance, and it is said fondly — the afternoon went somewhere and you did not mind where. Keep track is the other half of the pair, and it is the half you use about a spreadsheet.