I was diagnosed with borderline hypertension at age 28. After recording my bp twice daily for 30 days my average was 140/90 so my doc put me on atenolol 50mg daily. I also suffer with anxiety, panic attacks and stress(still do!). I changed my diet, exercised regularly, etc. My bp now is 110/70(or lower) average on 25mg atenolol(lowered it this year because the 50mg was dropping my pulse and bp too low). Some people develop high bp for no apparent reason. You said you have a lot of stress and some panic attacks which means you could possibly have anxiety disorder all of these can raise your bp. Of course changing your diet is good. Eat lots of veggies and fruits, less meat especially red meat and fatty or fried meats, eat more fish, hold the salt and processed foods, eat whole grains. Do you take any supplements? I've noticed since starting magnesium, calcium, fish oils and garlic my bp has gone down as it was standing at about 125/80 with the 50mg atenolol and now it's 110/70 with 25mg atenolol. You need to make sure you're getting adequate potassium also and at the very least 64oz of water everyday(more is better). Caffiene can also raise your bp so if you're drinking a lot of coffee, tea or soft drinks you might want to switch to decaf. The only time my bp rises now is when I exercise which I guess is normal.
Don't let it go though, definetly work with your doctor even if you decide to try changing your eating habits first, make sure you keep in touch with your doc and be monitored. I'm sure you'll get more advice but just thought I'd throw my 2 cents in
Take Care,
Tori