Believe it or not I did this same thing IN BASIC TRAINING once back in 2010 when I was 19.

A Colonel and Major walked into the bathroom while I was washing my hands, and as a scared shitless fuzzy patch E-1 with ADHD I forgot my M16A3 leaning against the wall by the blow dryer… for about 3 or 4 minutes, then as I was in a dead sprint back to the bathroom, I saw them walking towards me holding it.

I got smoked for almost 2 hours for that little slip up. I think they liked me because that was a light punishment for leaving your weapon behind.