Exporting search results to excel in ASP.NET MVC has slowed down the whole application

//Session["SearchResults"] = aPPET.ToList<APPET>();

public class APPET1Controller : Controller
{
   private APContext db = new APContext();

// GET: APPET1
public ActionResult Index(string search, string cagecode, string sortBy, 
                          int? page, string docNumber, string remark, string status)
{
    APPETViewModel viewModel = new APPETViewModel();

    var aPPET1 = db.APPET1.Include(t =>T.APPETMedia)
                                .Include(t => t.Status)
                                .Include(t => t.APPETCCode)
                                .Include(t => t.APPETDType);
             ............some more codes..............

    DateTime searchDate;
    if (!String.IsNullOrEmpty(search))
    {
        bool isDateSearch = DateTime.TryParse(search, out searchDate);
        if (isDateSearch)
        {
            aPPET1 = aPPET1.Where(s => s.Date_Received == searchDate);
        }

        else
        {
            aPPET1 = aPPET1.Where(t.Doc_Number.Contains(search)
                    || t.Status.Status1.Contains(search)
                    || t.Remark.Contains(search)
                    || t.CCode.Contains(search));
         ..............some more codes..............
           viewModel.Search = search;
        }

    }
  var stats = db.Status.Select(s => s.Status1);
    viewModel.Statuses = new SelectList(stats);
    {

      if (!String.IsNullOrEmpty(status))
      {
        aPPET1 = aPPET1.Where(t => t.Status.Status1.Contains(status));
      }
    }
    if (!String.IsNullOrEmpty(docNumber))
    {   
        aPPET1 = aPPET1.Where(t => t.Doc_Number.Contains(docNumber));
    }
    if (!String.IsNullOrEmpty(remark))
    {
        aPPET1 = aPPET1.Where(t => t.Remark.Contains(remark));
    }
 ............some more codes.........

    Session["SearchResults"] = aPPET.ToList<APPET>();
    return View(viewModel);

}

public ActionResult ExportToExcel()
        {
var AppetList= (List<APPET1>)Session["SearchResults"];
            var result = from r in AppetList
                         select new
                         {
                             DocNumber = r.DocNum,
                             Status = r.Status.Status1,
                             Remark = r.Remark
                       -----some more codes------

                         };
            GridView gv = new GridView();
            gv.DataSource = result.ToList();
            gv.DataBind();
            Response.ClearContent();
            Response.Buffer = true;
            Response.AddHeader("content-disposition", "attachment; filename=TaciList.xls");
            Response.ContentType = "application/vnd.openxmlformats-officedocument.spreadsheetml.sheet";
            Response.Charset = "";
            StringWriter sw = new StringWriter();
            HtmlTextWriter htw = new HtmlTextWriter(sw);
            gv.RenderControl(htw);
            Response.Output.Write(sw.ToString());
            Response.Flush();
            Response.End();

            return RedirectToAction("Index");