Psychological / emotional perspective: We can become conscious of deliberate falsehood in dreams when our emotions are called into question and we are not true to our principles.
To be lying prone suggests that we should adopt a different perspective.
[1]Material aspects: In waking life there is lying by commission and lying by omission; this is a deliberate manipulation of the truth. Dreams can often help us to clarify our awareness. We often can rely only on intuition to reveal the real truth.
[2]To lie, as in speak falsely, is to speak against a truth, though interestingly not necessarily against what we believe to be true.
If we have sworn to tell the truth and do not, this would be spiritual perjury.
[3]