I have had one major "experience," which defined itself as seeing that "everything is full of nothing" (as I expressed it at the time). It arose directly from spontaneously asking myself the question "Am I perhaps not just one single thing? Then POW, a shift happened.
It arose upon reading something from Douglas Harding (The "headless" guy). He wrote about how we would be seen in a photo taken from a distance of six feet. It's what we all think about when we think of a person. But then he presented the idea that we could be photographed from ALL distances, and it would still be us. So, if we were seen at a galactic distance we would "be" the galaxy. If we were seen from a sub-atomic distance we would be essentially nothing (because atoms are 99.9% "nothing"). I sort of momentarily accepted the idea that we were just as much the galaxy as we were nothing, I asked the question, and....lol...the answer was there to see.
Since then I try to keep aware of myself as the "witness," by recalling the phrase "It happens by itself" in ALL circumstances -- from getting lost in thought, to any circumstance which occurs. It's a very easy "summary" of the fact that I am consciousness.