Tail Down is an unusual occurrence as Parrots normally hold their tail in a neural position between the two muscle sets that either lift or drop the tail for flight control.
A pumping action helps a Parrot with an air sack (lungs) infection as a means of pumping air in and out. A dropped tail requires the release of the upper muscles and the tightening of the lower muscle, which implies (as referred above) a possible problem with the vent region.
If your Parrot's tail does not return to a neural position, by Sunday afternoon, be at your Avian Medical Professional on Monday.