Most certainly looks like there are different levels, or states, comparable to what science assumes about sleep. Maybe there are even more levels than the two we now know of.
Think only Regina said, one can’t die in a sleeping curse – but to me it sounded more like an attempt to reassure Henry, not like she was actually sure about it (didn’t seem to know much about it in the first place, besides how to cast it). Possible so far it never happened, but doesn’t mean it can’t. More likely considering the burns it is possible.
To induce the pain that it feels like it burned would be rather easy (stimulating the right nerves the right way). More complicate and in our scientifical understanding impossible to actually inflict real wounds via hurting the soul in another world or reality. Has to do a lot with believing, I am sure. What of course now might raise some other questions.
Snow showed some doubts in that fire room. Have a feeling, that she and Charming couldn't touch, because both or one of them didn't truly believe it was possible. Additionally Snow was starting to wake up.
¯\_(?????? ?)_/¯