Daily painful headache that comes and goes after 3 hour panic attack in january. no other symptoms. anything serious?

Headache is one of: 33 symptoms of anxiety. Having it continue for months after one 3 hour panic attack is not the norm, so go to an MD for a look-see. However, you might be suffering from residual effects, or sub-panic (chronic, low level anxiety) that could very easily produce headaches. Try massage, meditation, yoga. Here's another source: http://www.psychologyproductsandservices.com/page2.html