it had happened that to me mate too....I was moblising a 75 year male's neck (NO MANIPULATION i swear loool) and 1 day after the session he had Vertebral artery signs like blurred vision,dizziness and drop attacks....I t was a huge pitfall for me, because when i first took his history he denied any symptoms like that in the past....Then i thought,that we really must be cautious when we "generate" FORCES(simple mobilisation and overpressures to manipulation and thrusts) to the patient....Its always better for the patient to start with his own FORCES (self-mobilisation), and then consider further progression