I've suffered with severe GAD ever since I was 18 (currently 26). Once I saw Royce air ball those free throws I knew exactly what he had. I played bball in high school and was about a 90% free throw shooter until senior year when anxiety hit me like a ton of bricks. I probably shot about 33% from the line and air balled about half my free throws that year. As soon as I would step up to the line I could feel everyone's eyes on me and I was trembling so hard that I couldn't even manage to get the ball to the rim.
I deal with this 24/7 now, but my main panic attacks happen during social situations or when anything out of the ordinary happens. I shake horribly, heart pounding, adrenaline pumping, struggle to breathe, just complete panic like how you'd feel if you were being stared down by a lion ready to attack you. It really takes its toll on relationships with friends/family.
I had been trying to deal with this myself until I finally decided to go to my doctor about a year ago. I'm on medicines now which have helped a lot, but I think it will take some time figuring out the right meds and doseages.
I'd just encourage anyone feeling these types of symptoms to go and talk to their doctor about it and not feel embarrased.