How to overcome zzzzzz?

Buzz off: dididididi….
The alert sound repeated and the doors of MRT were closing. Out of sudden, I was awakened not truly by the buzzing sound but I regained my awareness that I got to reach my destination on time.
At once and without hesistation, I jumped out of my seat and dashed out of the door and safely. The story continued. The doors on the opposite train were about to close too and there again I dashed in.
I had been truly exhausted over the days but I was amazed at how self-aware I could be.
Being physically tired at most times, it was indeed challenging for me to stay awake when reading the Yoga theory, in particular the muscles, something not easily understood and could be rather confusing at times. So I dozed off most of the times.
How? I cannot go on in this way.
One day in library, after dozing off a few times. I decided that is enough. I remembered that day when Master Paalu told us to come closed to him but to listen to his Ujjayi breathing. I replicated and produced powerful ocean sound in both inhale and exhale. The folks around me could be pondering why the library sounded like an ocean.
I was simply amazed, I was cured! In fact, I had become more attentive.
So stay aware and be aware of your senses, your breathing.
Boon Chai