What can i do to stop a panic attack?

Difficult: You must be quick, as there rapidly is an "off-the-cliff" point where self-help techniques can't overcome the tidal wave. Controlled / concentrated breathing techniques; positive phrase repitition; biofeedback; (temporary) situation avoidance (if possible), are a few options. A good therapist/psychologist can help give you "tools for your toolbox" to use when coming on. Good luck!