Can a Panic attack last a whole day?

I started having general anxiety on the way to work this morning about 7:30am. About 8:15 the panic attack ensued. I took a Valium and the symptoms went away for about an hour. They returned but not as bad. Took a nap on lunch break and they seemed find, but re-returned a while later. Its now almost 8pm an this has been going on all day, I have been close to going to the ER for the fear of my heart stopping as it has been fluttering all day. Please Help