Dealing with Social Anxiety: Tips for Not Overthinking and Shutting Down

Usually, I tend to overthink on awkward moments long after the event happened. But tonight, because I was stuck in a car w/ my co-worker for an hour, when I tried to talk to them to get my mind of it, I shut down. I was at a complete loss of words, and I tried to play it off as a result of a headache/migraine I'd been having all day, but I just felt really uncomfortable overall because I couldn't think straight and I felt overwhelmed (not to a point of crying like I did in the past) and felt even more awkward/overwhelmed because of that. any tips on not overthinking as much/not shutting down?