Does anyone else find that they can exercise without any or much TN pain?

I managed to run 20 miles this morning and although it was hard getting motivated to go with the medication that makes me sleepy I found I was pretty much pain free for the whole 3.5 hours I was out! As soon as I had finished it started to come back again and I needed codeine but it was nice to be free of it for a few hours!

Does anyone else find this or know why it happens?