After I heard that the human race may cause its own extinction, I couldn't stay calm.
I'm kinda surprised myself, but I actually feel amazingly serene now.
I easily lose my calm when I’m constipated.
A place that is peace and quiet is a very calm and serene place. Ahh, so nice!
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.