What to do if you are having a panic attack?

I am having a slight panic attack as we speak… It feels as though my heart is beating faster, I’m a bit fidgety. I tried to go to sleep, but I can’t and lying down makes me feel worse. I am trying to stop it before it escalates. Are there any quick suggestions that I can do right now? Are there any medicines I should have on standby if this happens in the future, as from time to time I am prone to these attacks.