When is it not worth going to bed?

How little sleep must you be facing before you're better off just staying up all night?

I face this question more often than I like, but so far, my answer is that any sleep is better than none.

I'll be testing that answer again tonight, because I have to leave the hotel in less than four hours and I'm nowhere near ready for bed.

You know you're tired when your dreams focus on you sleeping.