What are possible complications of subdural bleeding?

Variable. From none to chronic headache, focal deficits, increased pressure on brain, seizure, dementia etc etc.
Emergency? Could well be an asymptomatic finding in pts on anti-coagulants, but could initially cause headaches, perhaps unilateral weakness, or leg weakness, and could expand with a catastrophic brain herniation (life threatening). In elderly, may see cognitive loss and confusion. Might contribute to seizures. Hospitalization with cafeful monitoring advised in most cases.