You have to maintain a reference to the 1st panel in the second if you want to do this: Create a class level Panel varaiable and where you hide the panel, save the reference to the panel you just hid. You can then use this to show the panel later.
private Panel myOtherPanel = null;
...
theOtherPanel.Visible = false;
myOtherPanel = theOtherPanel;
...
if (myOtherPanel != null)
{
myOtherPanel.Visible = true;
}