There is some mention of laughing and crying during panic attacks in articles trying to peddle cures. Some mention laughing and crying with Bipolar and GAD. The sites that follow do not list laughing and crying as symptoms. I expect the abatement of the attack has brought out both.

http://www.mayoclinic.com/health/pan...8/METHOD=print
http://www.psychologytoday.com/condi...panic-disorder
http://www.nimh.nih.gov/health/topic...er/index.shtml