The opposite of sober. When you have some mind-altering substance within you but not enough to be considered "high" or "drunk" and are still functional.
"Wanna get drunk?"
"Naw, I have to work tomorrow. But I could get a little unsober!"
It refers to psycho-physiological condition in which you can barely keep your eyes open and walk straight due to no sleep and excess alcohol and still end up assisting people with their stuff.
When flying from New Orleans to Detroit, i managed to help people out with issues regarding their tickets and luggage which proves i was unsober and not drunk. Lol.