2mg is quite a high dose if you have no tolerance, 0.5mg would be better if that is the case. If you do have a tolerance, then taking your normal dose should be fine. Be careful not to mix it with any other downers though (opioids, alcohol etc).
Make sure you drink plenty of fluids, try to eat something and get some rest too - if you are at the stage of getting panic attacks then perhaps you should reconsider how much you do? I appreciate you said you don't do much, but panic attacks and vasoconstriction aren't fun..