Blacked Out Disk Silently Traverses Canyon.While on a mule deer hunt, at approximately 0300, I woke due to digestive issues. I started walking toward the bathroom which was located north of the truck I was sleeping in. While walking, I looked up at the sky.The sky was overcast with altocumulus, turning into altostratus. The moon was waning, about half full, which was located behind my travel of direction. The clouds were not thick enough to block moonlight, which made the clouds very visible.While I looked up, I saw a blacked out disk silhouetted against the clouds, no lights, traveling at a high rate of speed from the NW, heading SE. I estimated the speed at about 500MPH. Similar to an F16 on a strafe run. The objects altitude I guessed to be 1000ft above ground level. After the object disappeared over the canyon rim, I looked for a follow up disk, which did not appear. The object never made a sound.I proceeded along my way as if I saw nothing. Until now, I had completely forgot about the event. This is what I find strange. I am a former Meteorological Observer, trained by the US Military. I have seen just about all military aircraft fly both in daylight and night. This was not one of ours. Why then, did I not act excited or scared by what I observed, or even remember the event till 6 months later? I treated it like a mundane viewing of an A10.Has anyone else had an experience similar to this? My meaning, observing something like a ufo, and acting like you didn't care about it, then forgetting the sighting. I had always wanted to see something I couldn't explain. My reaction is not what I expected it to be.