in order to have any commerce with other human beings I had to feel as though I was lying slightly about something all the time

I relate to this:

I constantly find myself saying

"I have a migraine" or "I have a headache" when what I really mean is one or more of:
- brainfog;
- mental exhaustion;
- emotional overload;
- Anxiety;
- PTSD;
- aphasia

that causes me to need not to and/or be unable to talk to

the taxi driver;
cashier;
person in line in front of me at the grocery store;
person on the bus/train.

I do genuinely get migraines, but often "I have a migraine" means "I am incapacitated for another reason which is harder to explain and which you may not accept/believe"