Use of “About to”

मैं जाने ही वाला हूँ 
I am about to go.

— It means that the work is going to be completed very soon.
When you called me yesterday, I was about to sleep.

— it means if the caller would not have called for few more minutes, he would not have got the opportunity to talk with the called person.
Confirm me fast, I am about to leave for my flight or you can send me a text.

मैं जाने वाला हूँ
I am going to go.