choking

I need to get to this special healing spot, in the woods. Before I can
get there I have to go through the swamp. As I wade through the
shallows, I get the feeling like this is a special initiation. I leave
some of my stuff behind, and take off my jumper as I don't want it to
get muddy. When I put it down by this tree, I see this strange slimy
growth in the swamp by the tree that moves, and covers my jumper in
mud. All of a sudden this choking invisible gas rises from the swamp,
and I can't breathe. I gasp for breath and wake up.