Practice practice practice. Just like everything else.
Did you really need a psychiatrist to tell you you had anxiety issues?
This sorta stuff you kinda know on your own.. if you don't its probably not -that- bad.
Anyway, drawing in public is always hard with people everywhere, stuff moving, colors everywhere, sexy women wagging their tails.. lots of distractions, these dont necessarily help you get your art game going.
So you just gotta practice it, go out where you want to sit, take out your sketchbook and start scribbling some terrible awful HORRIFICALLY bad sketches.
After a while, they'll start to turn into not so terrible sketches..
And if you keep at it for a while you might even reach your normal level.
It's okay to do bad sketches, bad paintings etc.
My sketchbook has about 10pages that don't look like complete garbage.
My SB here on CA is FULL of crap that I shake my head whenever I look at it.
But it's okay. Just stop caring about what other people think.
It's harder -said- than done.
For each failed painting/sketch you make, your exp gets doubled.
"Sadly, most artists prefer to give the elite their attention."