How do I stop panic attacks from happening? self harm invol.

Help. I've had a few bad ones that have been causing problems in my relationship because it makes it hard to talk about difficult issues. Last night I had a pretty bad one after not having any attacks for a while. I blacked out for a few seconds and hurt myself a bit by grabing a *mod edit* , altough I didn't remember that untill later that night after thinking about it for a while. I gotta say it freaked me out quite a lot. I've tried a variety of methods but I obviously relapsed. I think I need to get to the root of it and would appreciate some pointers. Thanks