To what does 身体的反应能力 refer here?
I think it's better translated as neural response than literally 'bodily reaction' since the neural system controls the reaction of the body.

I'm not a neurologist, but I do have that feeling that if I had a quarrel with someone, I would need some time to restore my spirits, In that period, my reaction to outside circumstance slows down a lot, I'm distressed, distracted and thus can't focus, perhaps some nervous substances not working as usual?

You can imagine that if you quarrel with you GF, even someone throw something at you you wouldn't care that much or you couldn't even feel that.