How come you’re always so calm?
The princess is a type of person who wouldn't get upset even if she lost her pet puppy.
My husband was fired, but I’m surprisingly calm.
You have a flat energy. What kind of energy would be a flat one? Probably a cool or calm one. You'd also tell people about this flat energy by saying you are all right or just okay.
This is a jukugo word, which usually means on'yomi readings from the kanji. If you know the readings of your kanji you'll know how to read this as well.