Checklists and checklists there a lot of them.
Below is one you can you use when you are going flying, if can help you decide if you should even go flying or stay home and reschedule.
I Illness
M Medication
S Stress
A Alcohol
F Fatigue
E Emotion
There are so many factors that determine if you should fly and just as many that should ground you for the day. That feeling of being in an airplane and wishing you were on the ground is one we all experience but should minimize, flying is something that requires all of your faculties. The items on the above checklist will affect your abilities, only you know your personal limitations, you are pilot in command - saying no before you go can be a hard decision but is a smart one.
The below checklist is an awesome one that expands on the above - print it out and fill in the blanks for your own limits.
http://www.faa.gov/education_research/training/fits/guidance/media/personal%20minimums%20checklist.pdf
