When someone tells you that you “look tired”, what exactly are they seeing?

Question

I know things like dark circles or bags under the eye can indicate tiredness, but what is the body doing to make it happen?

In: Biology

Answer 1

One thing that tells me when someone looks tired is when they behave less excitedly or less energetically than they usually do. Or when they seems to not be paying attention to what I am saying is another example. Its more about behaviour than looks.