Personally: "Check you've taken your medication, exercised, eaten and slept sufficiently before giving bad feelings credence."

That's a good one, but I've sometimes overdone that, and ended up blaming my sleep deprivation/stress/mental fatigue/hunger/dehydration/drunkedness/the temperature/whatever for poor choices I've made (which doesn't usually explain why I erred in that particular direction, rather than any other possible one) as a rationalization to avoid dealing with the ugh field surrounding the actual reasons for my behaviour.

All the variables that affect my mental performance aren't usually all at their optimal values at the same time, and I'd better deal with that.