Night vision is a measure of how sensitive your eyes are at low levels of light. Some people can function well under low light conditions, and others cannot. It may be a function of how sensitive the retina of the eye is and how the brain interprets low level signals differently. Things seem to move in slow motion under low light conditions. Distance and depth perception can also be thrown off at night.
Peripheral vision is a measure of your visual angle, or how wide your field of vision is. When we look directly at something, we are also aware of surrounding items even though we are not focused on them. They are blurry but still visible. Some people have a vary narrow field of view, and must constantly shift their view to detect moving objects to either side. Others can stare straight ahead and see movement to their sides without moving their eyes to look in that direction.
Situational awareness is a measure of how often you reevaluate all of the elements of a situation. For most people, their "situation" rarely changes quickly, and so subtle changes can creep into a situation without being noticed. Sitting at a desk working on a single task can allow time slip away, others to move around you, and other changes without you noticing them. When in a dynamic situation like flying an aircraft, things can happen quickly. A pilot is trained to constantly check altitude and airspeed, engine and fuel gauges, compass and direction indicators.
It is hard to identify a time where my life was saved because there is no way to know what would have happened otherwise. I think I save my own life every day by using my night vision, peripheral vision, and situational awareness driving home from work. Most people are concentrating on the cell phone or radio or make up or anything else other than driving. I don't know how many accidents I have avoided, by dodging multiple lane shifters, lane drifters, and speeders that I move out of the way of. I use the skills I learned in pilot training, to keep them all from bumping into me.
Using these skills correctly keeps your life from being in danger, so that you do not need to save your own life. As a pilot, I needed to make a night landing at a rural airport, but I could not get the runway lights to come on. The were supposed to respond to a certain radio signal, but nothing was happening. I had followed my course, but I could have been in the wrong area. It is difficult to navigate at night visually. Roads begin to look the same. I was circling in the area I thought the airfield was in, but could not see it. As I maneuvered toward my alternate landing field, I caught the runway lights out of the corner of my eye. I had been circling directly over the field, and so could not see it. I had left enough fuel to make it to my alternate field and to turn back and land at my original destination. I don't know if my life was saved that night, but I was heavily dependent on my night vision, peripheral vision, and situational awareness that night.
I hope this helps.