How can I calm myself down when I'm having a panic attack?

My life has been pretty hectic since I was about 12 yrs old, I'm a very tough girl & handle any negative situations very well. I am now 22 and have experienced the loss of my grandma & a miscarriage both in April. Which caused me to drop out of college cause I started having these very frightening panic attacks. If anyone has ever had one, it's very scary and makes you completely shut down where ever you are. I need to find a way to calm myself down, I already know what they feel like & what I think after it's gone away.. I've accepted the whole process & they are gradually going away. But I want to be prepared just in case it happens again. (Note that, I refuse to take any medications, I want to mentally be able to get over this & I have been keeping this a secret from my loved ones & the boyfriend I live with.)