When I was maybe 12 or 13, I woke up after having a nightmare and just sat in bed for a while, trying to remember what the dream was about. I was sitting up in bed, and for some reason I drew back the curtains to look outside. My back yard was filled with floating balls of light, which seemed to be larger than a softball. Occasionally the lights would flare up and glow even brighter. I just stared transfixed for a while, I couldn't believe I was awake.
The next day I was walking home in the early evening hours and saw fireflies floating near my house, and I realized that was what I had been seeing. I think my pupils were so sensitive from being in my pitch-black room that I could actually see the fireflies' bioluminescence in between light flashes.
Scattering caused by mist could have made them look bigger, or perhaps you were myopic?
This is a kind of "X files" thread.
Post experiences which spooked you, which made you doubt reality, mathematical or physical laws, your sanity, memory or perception. The more improbable the better, but no second-hand legends please, share only what you personally experienced. If you had the event later explained rationally please use rot13 to avoid spoilers.