Confident turned really really anxious

Well that stems from your previous worries of anxiety -- you might've been confident socialising but clearly those other things were worrying you to a point where you couldn't ignore them. No surprise that many negative things have manifested themselves in the positive aspect and you don't know how to deal with it. The best way to deal with this is taking a compassion-based approach; telling yourself that, for example, you're sort of feeling 'off' -- but that's okay. You're not speaking as much today, but that's okay. You obviously are good enough otherwise you would have no friends. There's nothing bad about you or your character

Your friends saw you red, but that's okay -- laugh about it instead of thinking there's actually something bad. Because really, when you think about it, it's not really bad is it? Your friends won't abandon you or anything.

Only by positive reinforcement and keeping your mind in a kind state will you become less anxious and feel better around people again

And if this has been for a while then you might want to look into a therapist who should help you with a very effective CBT-based treatment

I'd say from experience that these sorts of events can trigger a negative spiral, so the best course of action is to think positively and then you will act positively, reinforce your comfort.