The way you have drawn it up here, it looks like you are shorting the 5 volts through some resistor while trying to measure GND with an analog input and the interrupt pin.
That will never work.
Instead you can add another resistor between the analog pin and GND.
You'll create a voltage divider that way, and now you can actually read voltages using your analog input.
Golly, I can't even make a proper ASCII art picture ... that resistor was there on my scribbling paper; sorry for the confusion; and then it resembles the second circuit by Magician (see above). I don't understand how his first circuit works though. Maybe I take the route suggested by Retrolefty:
Retrolefty has offered you a gem, setting a fixed interrupt that you can use to acquire the analog value and any changes in that.
That interrupt doesn't need to be triggered by an external event, so it wil save you an input as well.
Of course you might have to take in consideration that this also uses some time.
So if your sketch has some dependance on timing, you should check that out.
I downloaded the code and see if I need it all; thanks for the suggestion (also to Retrolefty). My sketch performs 'commands' either read from USB or a WiFi antenna or from a file (I have an SD card attached); every pass through the loop() function performs at most one command; in between those switches need to be read ...