If you turn off ScreenUpdating before the operation, and back on
afterwards, then the user won't see that there's a hidden sheet.
Truthfully though, even with screenupdating on most operations happen
so fast that the user wouldn't detect them anyway.

Application.ScreenUpdating = False
ActiveWorkbook.Sheets("YourHiddenSheet").Visible = True
'
' Your actions here
'
ActiveWorkbook.Sheets("YourHiddenSheet").Visible = False
Application.ScreenUpdating = True