IAMA brain surgery survivor and I no longer feel fear because my right amygdala was removed along with 10% of my brain.
Edit: Alright that's it for me, I can't believe I just spent 4 hours answering questions haha but it's been fun. Here's some proof:   Also here is some [maybe NSFW? Just scars and brain bits] pictures of my brain surgery: https://imgur.com/a/6LoWKEx
I had my right amygdala removed along with my right hippocampus and the front (anterior) half of my right temporal lobe. I had two brain surgeries, one to place probes deep in my brain to record my seizures over 7 days, and the other to remove the parts that were generating seizures.
Among several other less-interesting changes like becoming more talkative and having a worse sense of direction, I noticed that I no longer feel fear. That doesn't mean I will calmly walk off of a cliff, just that my reason to not-walk off of a cliff is no longer precisely "fear." I am still capable of stress and anxiety, so when I say "fear" I am expressing a very specific feeling. I'll post the long story here and it may answer many of your questions:
It's important for me to define "fear". We use many other emotional terms interchangeably for feelings that are actually quite different. There is a distinct difference between fear, stress, and anxiety. Are you "scared" that you might make the wrong choice (say the wrong thing, buy the wrong product) the same way that you are "scared" if someone were to point a gun to your face? In order to discuss the lack of "fear' let's define those as different feelings, not just different levels of the same feeling. I'd call the former "stress", and the one I lost is the latter. Thus, if someone were to point a gun in my face I wouldn't be chilling. I imagine I would be VERY "stressed", like the feeling of "I just started on the last question of the final exam and I only have 30 seconds left!", but not "afraid."
The biggest way this has presented itself, having not had a gun pointed in my face, is the fear of my inevitable death. I used to have a hyperbolic fear of my inevitable death, but I still would take risks like skydiving. Perhaps it was the control that I wanted. I would think "I will die one day and there's nothing I can do about it" every 7 seconds for hours. Now that's completely gone. I am just apathetic about my inevitable death. Perhaps a more relatable example would be cliff-edges? I am able to go much closer to the edge of a cliff than I used to, but if I get too close I still feel that "make the wrong choice" feeling, closer to stress/anxiety than the fear I used to feel.
Finally, for those interested, I'll provide a quick rundown of which part does what in the average (right-handed & neurotypical) brain:
Right amygdala: Fear, physical response to negative stimuli (including the "fight or flight" feeling), harm avoidance, speech-inhibition (how much you have to want to talk before you start tallking).
Right temporal lobe: Recognizing faces, spatial memory (retracing your steps in space, like where you came from and where you put something), verbal intonation, object recognition.
Right hippocampus: Forming of episodic memories for the right-hemisphere. e.g. "[Who] did [what] at the [where] [when] because [why]."