'der folgende Code stammt von >>>Ullrich Schwarz<<<
'ich habe nur 2 kleine, unbedeutende Änderungen vorgenommen

'in Klasse1:

Public WithEvents app As Application

Private Sub app_SheetDeactivate(ByVal Sh As Object)
Set LastSheet = Sh
End Sub

Private Sub app_WorkbookDeactivate(ByVal Wb As Excel.Workbook)
Set LastSheet = Wb.ActiveSheet
End Sub

'in Modul1:

Public LastSheet

Sub Rücksprung()
On Error Resume Next
If Not IsEmpty(LastSheet) Then LastSheet.Activate
End Sub

'in DieseArbeitsmappe:

Dim appObject As New Klasse1

Private Sub Workbook_Open()
Set appObject.app = Application
End Sub