fear is brain reaction to danger you face, fear makes our body react quickly, for example if you see a lion coming towards you, you will scream automatically, because it can scare the the predator and your heart will start beating fast and makes your body to act faster and stronger, so that you could run faster and climb on the tree quickly.

Inflammation of the amygdala.

How you respond to fear is a choice, but fear itself is instinctive.

Danger is real, you bet. But if you don't respond to fear, the result can be very real too.

That seems to be the Viking Ragnar faced with a monster. I've just been reading Beowulf who had to face three monsters in his lifetime.

Yes indeed!
I stopped getting nightmares after I became an atheist, it took away all the irrational fears

Fear is an emotion that readies the mind and body for a perceived threat to one's life... Whether real or imagined