What would you do if someone panicking during the boarding time?

First of all I would approach this passenger and try to find out what caused his/her panic attack, as sometimes it can be caused of some personal problems or stress. I would try to calm down this person, reassuring him/her about the safety onboard. As well I would give such person some water or green tea to make him/her relaxed, although I would check time to time if this person feels good and safe