Most of my life I've suffered from debilitating migraine headaches.
Now that you feel all sorry for me, here's the helpful scale I came up with for rating their intensity. It's pi-exponential so the pain slightly more than triples with each increment:
0: No pain, no gain
1: Slightly tense, no worries
2: Is that a headache coming on?
3: Push through; keep working
4: Starting to feel anxious about this
5: Just on the good side of bad
6: Get really distracting now
7: Remember to breathe
8: Take painkillers
9: With codeine
10: Call mom
11: Nausea, vomiting, want to die