Its not so much a case of thinking I have made X amount and then playing badly because of it - its more that you start feeling a bit too confident about your abilities over those of your opponents and so your play starts going downhill.

If we are talking about making +EV decisions and ending your session well, what should you be looking for as early warning signs that you might no longer be making +EV decisions and its time to take a break? (A list of things to look for would be very useful)