70% of people in the UK have sensory loss...I'm guessing...
Herpes labialis is what you are looking for
Excitatory neurotransmitter? This question is too vague.
body language, has he been acting weird? Agreeing or disagreeing in a joking way, lot of eye contact, complements you, the way he responds to touch (like a hand on his shoulder, holding his hand, ect.), and does he lean forward when your speaking to him despite already sitting close
