I see double/slanted when I look down with my head titled back!?

[Cammy1995]

So when I tilt my head far back and look down as much as I can, I slightly see a slanted/double layer coming from the left side, and as I slowly bring my head/eyes back to a straight line of view, it all merges becoming 'normal'. I'm concerned if what I'm experiencing is normal or not, I worry so much about this stuff....

(I'm 19/male).