I had a 2011 Macbook Air that would go blank randomly. After some investigation, I determined it was often when I was moving it from one place to another (sometimes even just repositioning on my lap), and that it was going to sleep, not completely crashing.

Of course, MBAs have no moving parts, and there were no rattles when I shook the machine and listened. Apple also could not figure it out. After replacing several parts, they eventually replaced the unit with a newer model (it was 2014 at the time).

Soon after getting my new MBA up and running, it experienced the exact same glitch. I knew it had to be something environmental, since the odds would be astronomical that they would have replaced my unit with one that had the same rare glitch. But I was traveling, which eliminated anything relating to my house, neighborhood, power lines, etc.

Then I looked at my wrist, on which I wore a Seiko Kinetic watch. It was triggering the magnetic lid-closure detector, which is on the sides of the base of the MBA. When I picked up my computer with my left hand (I'm right-handed, so this was less common), it would trip the sensor.

Interestingly, there is a very easy fix for this (and similar issues, mentioned in other comments in this thread), which is to only sleep the machine if both left AND right sensors are triggered. If it seems like the left side of the lid is closed and the right side is not closed, probably it's a false positive!