Let me try. Im not a professional so you dont have to listen to me. First off, im guessing you live in a flat area to get tornados. I think for tornados you have to go to a room with no windows. But either way, you will be fine. Just tell yourself "Im ok" several times. Try to calm down cuz you can't control it. If it were me, id be outside filming it, but you may not be able to. I live in a hilly area so our tornado warnings are a joke. I personally love the rain, and it calms me. Find something that calms you. Perhaps listening to music, or watching movies. Do something to kinda numb yourself to what's going on outside. Then when's its over, go outside and stand in the sunlight.
Dont try to control everything. Think about what you really need to do, and what you just think you need to do. Focus on one thing at a time. Dont worry, because there is nothing you can do.
Tell me if this helped you, I hope you get better, and anytime you need to talk, contact me.