the restaurant was nearby my area
Is there a reason you didn't go to it but chose to use grubhub? A walk to the restaurant to pick up food can be nice and help clear the head.
How is it that you can feel horrible when you’re hungry (physically and emotionally) and then feel content and all is right with the world after having eaten?
Because the contents of our stomach, the amount and variety of bacteria, pH level, quality of food, affect our mood. Often this gets us into a vicious cycle: eat junk food > feel like shit > eat more junk food, and so on. Junk food isn't only nutritiously poor, it is also full of preservatives and bacteria can't go grow on it, which means bacteria can't really grow in our stomach either. The food you ordered from the Vietnamese restaurant was probably a home-made recipe using regular supermarket ingredients, that's why it feels good for you to eat it.
And what did you all eat today (so far)?
I just made myself egg fried rice.
