Maybe it isn't about the remedy for the condition but about fitting the remedy for the person. You are treating a person - you - not a dis-ease.

Herbal teas are often not recommended in general broad mb suggestions. They have strong energies which most people don't respect. They can be utilised for deep healing if properly implemented. Chamomile tea is a nice after dinner drink but it can also be used for relaxation as you have discovered.
It is a flowering plant and therefore would be considered more yin than a herbal beverage made from the root of a plant. That doesn't mean we cant use it - being more yin doesn't make it less desirable just a property to be aware of.
perhaps it would be more helpful to look at foods and drinks as more or less appropriate for your current state rather than seeing things as inherently good or bad.
And the biggest test is how you feel. You mentioned you feel better.....keep watching and feeling....

what else is there to drink?!! lots -

umeboshi tea, dandelion tea, ginger tea, adzuki tea (great for adrenals) burdock tea, grain coffee, sweet veggies drink (very good for panic and to relax), corn tea, nettle tea, mu tea (very strengthening and warming) and many many more
so many teas, so little time!

chamomile is very high in minerals - like magnesium (see below) and calcium

and although some say there is caffeine in bancha - the twig only varieties (kukicha) have almost neglible caffeine - they are even given to kids.
you would probably absorb more caffeine from walking past Starbucks than a small cup of kukicha. You can make it very light - not even boil it - just pour hot water over it or use the tea bags from eden foods.
but listen to your body - if you react then don't drink it.
but truth - would you feel the reaction if you didn't think it had caffeint in it?

Magnesium and other mineral deficiency is a common cause of panic attacks. I would get my levels checked or play with a good magnesium supplement.

Breathing imbalances - often hidden are also related.

check out Breathing free by Theresa Hale. This goes with the magnesium issue and also make sure you consume enough but not too much unrefined whole sea salt.
Barley as a grain can be cooling but only ever so slightly. And if you have panic then a little more cooling won't hurt. Asa cooked grain the cooling effect is soothing but not excessive. If you are consuming it as tea - the barley is usually roasted which makes it more neutral or even slightly warming. I wouldn't get too caught up in the details. Tofu is cooling but when fried it is much less so. Your reaction could have been from any number of factors - the soy? the oil? any seasoning. Have some ume kuzu with ginger and relax about it all! That is a great remedy!

ilanit