AnimateWindow(Panel.Handle, 1000, aw_hide or AW_SLIDE OR AW_VER_POSITIVE);
panel.Visible:=false;
	
type
  TForm1 = class(TForm)
    ..
  private
    FPanelHeight: Integer;
    FPanelVisible: Boolean;
..

procedure TForm1.FormCreate(Sender: TObject);
begin
  FPanelHeight := Panel1.Height;
  Timer1.Enabled := False;
  Timer1.Interval := 10;
end;

procedure TForm1.Button1Click(Sender: TObject);
begin
  Timer1.Enabled := True;
  FPanelVisible := not FPanelVisible;
end;

procedure TForm1.Timer1Timer(Sender: TObject);
const
  Diff: array [Boolean] of Integer = (-1, 1);
begin
  Panel1.Height := Panel1.Height - Diff[FPanelVisible];
  Panel1.Visible := Panel1.Height > 0;
  Timer1.Enabled := (Panel1.Height > 0) and (Panel1.Height < FPanelHeight);
end;