how do i know if i have low blood sugar?

How long have you been feeling tired and low energy? How severe is this? (Please know, "can't stay awake" is a severe condition, and I assume you are speaking metaphorically that you are actually "really tired, sleepy or exhausted"?)

You would need a blood test to check your blood sugar. The symptoms of low blood sugar include:
* Weakness or shaking
* Moist skin, sweating
* Fast heartbeat
* Dizziness
* Sudden hunger
* Confusion
* Pale skin
* Numbness in mouth or tongue
* Irritability, nervousness
* Unsteadiness
* Nightmares, bad dreams, restless sleep.
(Source: Cleveland Clinic)

You said you "can't stay awake" and have "no energy", which sounds like something else...
- When did you last eat, and what did you eat?
- Do you typically eat a healthy, balanced meal every 2 hours (carb + protein, fresh fruit and vegetables, dairy or substitute?)
- How are you sleeping at night?
- Are you bored, irritated or frustrated at work (or with whatever you are doing)?
- Are you properly hydrated? How much water are you consuming?
- Any new medications or other changes in your life?