joann difede has worked with 9/11 survivors to overcome that stigma.in september 2001, she was treating burn patients with p.t.s.d. after 9-11, her work became all the more urgent. difede pioneered using virtual reality therapy to transport her patients back to the sights and sounds of that day. >> many people will tell you even to this day on a september day, and the sky gets a certain blue cast to it. they'll think if the world trade center, they learned that the blue sky was associated with a terrorist attack and something horrific and unimaginable. >> yang: by confronting their trauma, they were able to overcome it. >> so the process of learning the whole idea in these trauma simulations is you go over your trauma as if it were happening again in the present tense so that your brain starts to learn, you know, it's a september day. it's not it's not 9/11, 2001. >> yang: for many, the pandemic has meant a new kind of mental stress-- trauma that can be especially acute for frontline health care workers. >> 9/11 was such a short event, at least for us.