For me, I find tactile stimulation helpful!
There is something called TIPP
T- Temperature. Try splashing your face with cold water. Sometimes I will put an ice pack on my cheeks and take deep breaths. This will provoke a mammalian response that will slow your heart rate and breathing. (Just don't leave something really cold on one spot of your face for too long so you don't hurt yourself)
I- Intense Exercise. Not really the most practical if you're in public, but if you're home alone and freaking out, you can try doing jumping jacks or push ups. Makes it easier to get your mind off things.
P- Paced breathing. Pretty straightforward, try breathing in deeply, holding it for a little bit, and exhaling.
P- Progressive muscle relaxation. Purposefully tense a muscle group, and then relax it, ie, tense the right arm, and then purposefully relax it until it is limp.
The two Ps can be paired together to make it more effective. These do seem kinda silly but they work sometimes. Panic attacks really suck, so anything that works ig.