To indulge your last question, I have a reason for not drinking green tea you may be able to help…
Anders Mortensen

I’m no neurobiologist but it could be due to the“Catechins inhibit(ing) the enzyme COMT that degrades noradrenalin and cAMP”. The consequence of this is upped dopamine production which if significant can cause a consequent ‘crash’, ie the headache/migraine you reference.

This is just a layman’s best guess so DYOR!