What is the difference between Psychogenic Non-Epileptic Seizures (PNES) and Somatoform Disorder?

What is the difference between Psychogenic Non-Epileptic Seizures (PNES) and Somatoform Disorder?
I passout and have seizures and at times stop breathing during these spells.  I also have tremors.
I've been told that this is due to stress and PTSD.  This is so frustrating and my body can't take much more!