Exhaustion..

You know you're tired
when you reach home from IMDEX and plonk straight into bed..
You know you're exhausted
when you have so much trouble dragging yourself out of bed at 9pm..
You know you're exceptionally drained
when you thereafter fall back into sleep at midnight..

And the next day..

You can tell its chronic
when your normal breakfast isn't sufficient energy for your body
You can tell its persistent
when you edit a document three times and still get the price wrong
You can tell its detrimental
when your choice of food is focused on anything that gives you energy to keep awake....