Almost all of my experience has been solo, but it has largely been day hikes and 4 or 5 day excursions where I had a vehicle close at hand. (A lot easier to set up base camp out of the back of a Jeep)

Even with this half-hearted approach, I have experienced my mind playing tricks on me, especially on the overnights. I took one day hike in which I was packed for 2 hours, but ended up being out for over 6. The main thing is to be thoroughly prepared, and don't let your guard down even if you are familiar with the area. That is how my aforementioned 2 hour hike got much longer.