[simonster]

To expand on the uniqueness of the experience of suffocation: Suffocation is apparently the only experience that can produce fear in patients without an intact amygdala. In a recent study (http://www.nature.com/neuro/journal/v16/n3/full/nn.3323.html), researchers administered a mixture 35% CO2 and oxygen to three patients with bilateral amygdala damage and who could not recall experiencing fear in any decades for decades prior. All three had panic attacks. While it's thought that the amygdala contains CO2-sensitve chemoreceptors as this article states in the first paragraph, this behavioral result shows that other brain areas do too, and activation of these chemoreceptors is sufficient to produce fear even without the brain's "fear center."