allergy or psychosomatic?

If you go to your local homeopath they can run intolerance tests, as you may have an intolerance to caffeine or something. If not, then it probably is slightly psychosomatic because you have told yourself that you don't like it for so long that your body reacts. If you don't want to go to a homeopath, try drinking Rooibush (Red Bush) tea which is decaffeinated. If you still get the reaction, then it is unlikely to be an intolerance (but obviously this isn't a medical test!)

When you get this reaction, maybe try putting the cup down and doing some relaxation exercises as it may now have got to the point where your brain is expecting a reaction and so you sunconciously get anxious and tense. Deep breathing and changing the direction of your focus (such as going to the bathroom, going into a different room for a few minutes, watching a video on youtube) may help.