When i tilt my head forward & look down or lie on my stomach propped up on my elbows, my eyes feel pressure, & go cross-eyed. why is this?

Double vision?: Multiple sclerosis, myasthenia gravis, disorders in the cerebellum (the balance & coordination part of the brain) and in the connections between the brain, inner ear and eye muscles can potentially cause double vision. Based on the info you provided, you are already being evaluated for some kind of neuromuscular problem. I It's VERY IMPORTANT that you report this system to your doctor(s).