The one version of this that is not good news is worth learning now, because it looks superficially similar and means the opposite. Energetic fluttering is fine. Trembling or shivering while sitting still and fluffed up is not.
Birds cannot sweat, so a hot budgie holds the wings slightly away from the body, breathes with the beak open and sits quiet. Wings out plus open beak plus a warm room is heat, and heat stress in a bird is dangerous. Move him off a sunny windowsill and away from radiators.