Fiancé sees purple lights

Desiree • Due with my rainbow baby Aug 6th Derik J McMurray
So every now and then my fiancé will say he's seeing purple lights. 
He says it looks like lighting or a wave that goes sideways not up and down and it just appears.
It happens randomly no matter where we are or what we're doing. 
I believe that it's an energy but I then again I'm not really sure. I believe in energies but I've never experienced what he's been experiencing so I'm not familiar with it.
I want to help him but I don't know how.
Can anyone explain to me what's happening or what he's seeing?