I drink decaf tea and coffee, but I'm sure that there's something else
that has an effect (tannin?), cause after about 4 or 5 cups of decaf
tea I still end up feeling a bit frayed. There's still some caffeine
in decaf, but it should not be enough to have a noticeable effect.
Not sure what could cause that.

Any recommendations for types of tea or coffee that would be
relatively free of side-effects? I've tried Celestial Seasonings tea
with Rooibos...pretty good in its own way, but not reminiscent of
black tea.