Pavlov's dogs were conditioned to salivate when they hear the bell ringing before they even see the foods. You are conditioned to FEAR when you sit at the computer before the pain.
1 - Bell ringing = sitting at computer. (conditional stimulus)
2 - dogs salivating = you have negative emotion about sitting. (conditional respond)
3 - dogs got food = you got pain/tms symptoms (unconditioned stimulus)
When Pavlov keep ringing the bell but did not give dogs the food, after awhile, the dogs stop salivating when they hear the bell ringing. If you can somehow stop you mind from having any fear or any negative emotion or any negative expectation about sitting at the computer, after awhile, your pain will disappear. That is Extinction of the conditioned respond.
Reward yourself is not important. It is important to stop yourself from producing any negative feeling/emotion/thought/expectation... about sitting at the computer.
sitting is a normal human activity. It should not cause any pain unless your mind think of sitting as dangerous.
I hope this help.