OK, a new post after a long time of idleness, so I will try and sum up what we have so far.
Dreamwalkers are a people with the skill to enter others dreams and manipulate them to certain extents. The extent of manipulation can be determined by each individual user.
Entering the dream and exiting each require extensive skill and concentration, and a wrongful execution will awaken the dreamer while the walker is still inside.
In the case of the above event, the walker's mind is trapped in that of the dreamer, unable to control anything, but forced to submit to the dreamers will until he falls asleep again. The body of the walker remains, lifeless, as the mind has left it temporarily.
A dreamwalker is capable of killing the dreamer in the dream, which results in a death of the mind, so the person dies, but the walker must be exceedingly proficient at dreamwalking before this can happen.
A person who has been walked several times can learn to guard their dreams, and make entrances and manipulation harder, though exiting is always just as easy, unless the dreamer can train himself/herself to wake at any given time.
A walker or a person who can guard their dreams must be able to maintain awareness of their own dreams, to work their skills, or they will be swept away!