I used to get this. In tournaments I used to play well at the beginning and get far, then when I was in the money with a large stack I would start playing bad hands out of position, chasing more and risking more chips. I think you have to really look at your play when you become overconfident, to see where you are going wrong.

Just because you 2x buy in at table, or a large stack in a tournament doesn't mean you can play crap hands or play out of position.