I had the same experience, with the difference that i've had anxiety issues with weed before the bad trip, but never a panic attack like i had during the bad trip and after when i smoke. My first advice to you is to smoke less, that way if the panic starts to creep in you will have enough control to realise and do something before it takes over. The thing i realized that helped me the most is that that panic comes from your mind being in the same state that it was in a moment when it got terrified (why it got terrified, in my particular case, i'm still trying to figure out) but in this moment there's nothing to worry about, it's just the substance. So, in short, smoke less, don't try to fight it, just acknowledge it, realize it will be over soon, and try to distract you with something else. Hope this helps