I used to go down complete spirals when I had moments like these, but they have completely stopped since I started working in retail. Many times I've really messed up a sentence infront of a customer and felt so embarrassed, but then I kinda realised that it didn't really matter. Who are these people to me? Am I selling myself or a product? They leave the store eventually in the end anyways and I won't even recognise them again if they did return. Oh well!