This may sound a little out of left field, but have you ever been checked out for sleep apnea?
It is “a sleep disorder characterized by abnormal pauses in breathing or instances of abnormally low breathing, during sleep. Each pause in breathing, called an apnea, can last from a few seconds to minutes, and may occur 5 to 30 times or more an hour.”
“Regardless of type, an individual with sleep apnea is rarely aware of having difficulty breathing, even upon awakening. Sleep apnea is recognized as a problem by others witnessing the individual during episodes.”
“Sleep apnea should be considered a dangerous condition, which may lead to congestive heart failure and other pulmonary disease, as well as other complications of hypoxia.”
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2823279/
Patients with sleep apnea can report intense nightmares on waking from apneic events. Anecdotal examples from the author’s sleep medicine practice include:
“I am buried under the sand and fighting my way to a surface that I can’t seem to reach. I wake gasping for air.”
“I’m deep under water that is getting darker and darker. I’m holding my breath, but I can’t any longer. As I breathe in water, I try to scream, but there’s no sound. I wake up in a sweat.”
Thanks.