Excedrin contains CAFFEINE... and I think that this ingredient is the active one for it, which accounts for its popularity.

Caffeine itself is implicated in headache, because it causes a mild addiction, and rebound. When the caffeine wears off, from what you consumed during the day (and it doesn't take much--since I get this effect from one tea in the morning during the summers) it rebounds at night.

It just became very HOT here the past few days...and bingo,
there was my tea headache/neck thing. It would wake me up sleeping...throbbing away. So yesterday it was the beginning of no-tea, and I didn't get the pain in my neck!

People can be very different from each other.

I think the journal idea is excellent... you may learn alot.
If you have a blood pressure cuff, do that too. It is always revealing to log blood pressures!