Been lightheaded for months, daily almost all day. doctors still trying to find cause. was laying in bed and suddenly felt like i was going to passout. my vision went blank for a second as if my eyes shifted. what are the possibilities or cause?

Near syncope: This could be a heart rhythm disturbance that should evaluated - this may include an extended monitoring period (you can wear it as an outpatient) for your heart to try to capture the rhythm when you have symptoms. I would recommend you continue with an evaluation that would include this. If this evaluation does not indicate heart rhythm issues, stay with your doctor to find other causes.