I spoke to my doctor about it and she says it is a known phenomenon with age. They simply don't know why. Interestingly I did have a similar thing happen at 30 which I just remembered. Prior to 30 I had about 5 cups a day via work but I went away to school and had to stop that (because I didn't have a coffee machine) and afterward I could only have about 1 or two per day. I have discovered that having water can reduce the sensitivity.

Now that think about it a lot of people that are older than me do have decaf... but I always thought it was due to medication / health conditions.