I have had approx 3 spells in the last week where I either blacked out or came close to blacking out. I also have noticed that my blood pressure in my left arm is running extremely lower verses the right arm. I am also having headaches and some nausea.
Hello! Thank you for asking on Chat Doctor! I recommend you to perform a comprehensive medical check up to your doctor (GP or Internist), to rule out any subclavian artery blood circulation abnormalities; to investigate for a possible subclavian steal syn Chat Doctor.  An eventual Doppler ultrasound or even Anglo CT or MRI, angiography, is sometimes necessary to clarify the diagnosis. Hope to have been helpful to you. Greetings! 