What can cause feelings of passing out? i haven't felt right in 5 months now. had different tests, all negative.

Complex: You need a second opinion - consider seeing an electrophysiologist. You may need prolonged rhythm monitoring and a tilt test. Neurologic (non-cardiac) causes also need to be considered. The list is long and includes various causes of low bp, seizures, inner ear problems, vasodepressor spells but from a cardiac perspective, a rhythm disturbance must be definitively excluded.