[user104658]

On the psych side they can make you FEEL like they restrict your breathing because instinctually, if something is covering your nose and mouth, you want to remove it to be "on the safe side". It makes you anxious, you subconsciously start breathing heavily, and that's what makes it feel like it's hard to breathe. If you relax and breathe normally you're fine. It's a mind over matter thing.

Think of "Jimmy" in independence day (Will Smith's pilot friend). He's panicking and feels like he can't breathe, instinctively pulls off his mask (oxygen mask for pilots at altitude) and Will Smith is like "Put your mask back on! Jimmy! Jimmy nooooooOOoooOoOooo!!".... *ahem*... So yeah anyway it's the same principle. Jimmy could breathe with the mask on, Jimmy needed to keep his mask on, Jimmy panicked and felt restricted and pulled his mask off (not really realistic that a trained airforce pilot would to that, but creative license and all that) when actually he just needed to keep it on and breathe normally. Jimmy died

Its the same principle.