What is the meaning of saying that the consciousness of the past weighs like a nightmare on the brain of the living?

There is no such popular saying. Someone might have said it, but is not profound in any way. It would depend entirely on what the past consciousness was related to.

The realization that you messed up and can’t go back in time to fix the situation stays with you. Time only moves forward, and you cannot undo what you’ve done. You can ask for forgiveness and make restitution, but you can never make things that you’ve done in the past not happen.

it would be open to ones own experienaces so to me it means if you still care and no one can help that, you can never be truely free. its one of many simple explainations of the dilemma of life. what i love and helps me each day is the phenomenon of humour its the answer to lifes ironies of which i think your question is one. so laugh like a three year old till ya cry

It’s about fear of zombies.

Carl Jung springs to mind, ill spend my whole life trying to understand that guy

but thats another question all together