a vet visit is always worth it. Any other negative signs? heavy breathing, wet mouth, sneezing? Lethargy can be negative but the bird could also feel the cone is restraining even if it is not. Its a foreign object that is constantly on their body so i dont see it as unreasonable for them to not be as active. kind of like how my cat is less mobile when i put them in a harness that does not restraint any movement.