Imho you have to know yourself really well to decide whether you want to let it happen or not, because only you know what happens next. But if you have a game plan on what to do when you feel it happening, hopefully the panic will become less.

I would suggest to try to excuse yourself and take a moment or several moments alone or as long as it takes to get yourself together. Do some meditation/breathing exercises. I do difficult subtractions or something. Also try to focus your senses, touch, vision, hearing etc. So feel things with your hands and try to describe texture, what do you see, etcetra...It's actually very common to have something (oddly shaped and texured) with you for exactly that purpose.

It just so happens that I was in a group the other day and I could feel a panic attack coming on. There was no other way than to excuse myself. Meeting or no meeting. In my case dissociation would have either meant a) continue the meeting outside myself and suffer consequences at home or b) go bezerk at meeting.

When I'm at home I usually let it happen, because obviously there're something scary going on. Still, this can be particularly dangerous because I seem to have no control and no memory of what I have done. If this sound familiar to you, then please do as I say don't do as I do ;) (see /u/shinebrightlike for more useful advice on this particular subject)

Hope this helps.