Sit down (don't lie down) - and breath as slowly as you can into a brown paper bag.
Most drugs are about the worst things you can do for the panic attack itself, if you need anxiety medication - it should be taken in the normal course of your day.
The cool thing about a panic attack is that if you recognise two important aspects - you know nothing is really wrong.
1. The chances of everything in your body suddenly going wrong are pretty slim.
2. Panic attacks have a fairly short duration - 20-30 minutes, so you know there is a limit.
See your doctor - but I've been given advice to take a phenergan (anti-histamine) as well, because I also suffer from allergy attacks - the phenergan will attack the allergy if that is the cause, and attack the blood pressure and assist with sleep if a panic attack is the cause.