From my experience, saying "I'm thinking" actually makes it worse. Instead of thinking for a response, I internally start to panic (mainly thinking whether I have considered everything and the response is correct). After a few seconds of "thinking", I eventually give a response that is no different to my knee-jerk reaction.
I do find replying with an email to be extremely helpful. Even if the response is not correct, it does show you have put in the effort to reflect on the meeting after it has finished.
I do find replying with an email to be extremely helpful. Even if the response is not correct, it does show you have put in the effort to reflect on the meeting after it has finished.