I think it is possible to have negative energies take advantage of a weak mind. There is always a way out. One thought can set you free.
I don't think that these negative energies are outside of us. I think they are internal turmoil presenting itself in the form of a possession. Illusions of the mind and lost in it.
Enter the bardo with no illusions, no expectations, accepting of all and you enter with strength and will be shielded against these negative energies. We must prepare ourselves and protect ourselves when entering into alter states of consciousness. If we do not we are susceptible to manipulations of the mind. Falling into a world of illusion.
"In the universe there is an immeasurable, indescribable force which shamans call intent, and absolutely everything that exists in the entire cosmos is attached to intent by a connecting link." ~Carlos Castaneda