As the others have suggested, definately talk to the OB and midwives beforehand so that they will be aware.
There is also a phone app which is a ball which grows bigger and smaller and is specifically for people who experience panic attacks. You time your breathing in and out to the expanding ball on your phone and it gives you something to focus on and help you to breathe through a panic attack. I don't know the name, but I'm sure if you did a search, you'd find it. Most people aren't aware of others when they are experiencing a panic attack, it's not all that obvious to everybody else. Lots and lots of people experience them, probably more than you'd think, so don't feel that you're alone or that it's shameful or bad etc. The better informed your care providers are, the more understanding they will be.
Hope all goes well for you this time around and that you feel better supported in hospital.