Manage Session Timeout using ASP.net

I have two sessions in my code:

Session["Email"] for user Login Authentication

Session["prevUrl"] to remember last page visited

I want to know how to manage the session timeout . I only want the Session["Email"] to timeout so the user can be redirected to the last page visited when they log back in. At the moment both sessions are timing out after 1 min

Thanks

Web.config

 <sessionState mode="InProc" customProvider="DefaultSessionProvider" timeout="1">  
  sessionState>

Global.asax.cs

void Session_Start(object sender, EventArgs e) 
{
  // Code that runs when a new session is started  
   if (Session["prevUrl"] != null) 
   { 
    Response.Redirect((string)Session["prevUrl"]); //Will redirect to previous page visited
   } 
   else 
   { //Redirect to Login Page if Session is null & Expires   
     Response.Redirect("Login.aspx"); 
   } 
}

C# Page Load

 protected void Page_Load(object sender, EventArgs e) 
 { 
   Session["prevUrl"] = Request.Url;
  if (Session["Email"] == null) 
  { 
   Response.Redirect("Login.aspx"); 
  } 
 }