Weird experience during meditation

[Aureus]

The colours you see behind closed eyes are the colors of those energies you have the most of. So in the case of purple it's probably due to you drawing energy to your forehead. This happens naturally when you focus on the empty space behind the eyelids. One sign of an active pineal gland is a slight spinning motion in the center of your focus. Easier to see when it's dark.

Heaviness may be felt for several reasons, most likely because of the increase in earth energies.

I can't comment on the urge to shake your head.. But the things you've experienced are totally normal..