Can you expand on your definition of "lack of sleep"? Since sleep is something that isn't uniformly measurable and is both relative and subjective to the indivi

Can you expand on your definition of "lack of sleep"? Since sleep is something that isn't uniformly measurable and is both relative and subjective to the individual what are you measuring to consider it lacking? Sleep doesn't really work in the realm of arithmetic and there is no way to credit extra sleep because you slept in on Saturday so how can you "lack" sleep because you stayed up longer one night verse the previous night? What if you did an extra exercise that day are you now lacking sleep because you exerted yourself more?