Why does drain current decay after the peak in class E power amplifier?

I have been wondering why drain current decreases a little and then dramatically drops to zero after reaching the peak in class E power amplifier when the switching transistor is on. I understand that it is because the transistor is turned off so that the drain current starts dropping dramatically to zero. But what really causes the current to decay a little before the dramatic drop? I just cannot figure it out. I really need help!