Despair in a dream usually reflects a sense of being stuck -- exhaustion that's gone on long enough that the direction forward has become truly hard to see. Unlike ordinary sadness, despair in a dream often names a specific loss of momentum, a feeling that effort itself has stopped producing any visible change.
In the world many evils will happen, when in one month there shall happen an eclipse of both luminaries; chiefly in those places subject to the sign in which they happen. - William Lilly (1602.-1681.)