I was off the bike for 2 1/2 wks and the first thing I noticed was my climbing legs were - ummm - gone. It's been 2 wks since I"ve been back and on the bike again and they're coming back fairly quickly so yes you can lose the fitness but like CA said, your muscles will "remember" and come back quicker.
As for the eating like it's your last meal - I notice I do that when the days get shorter. I also crave more carbs. I'm guessing it has to do with that whole hibenation mode thing. I just make sure I have UV bulbs in the lamps I read under at night and I've added some Vit D to my regime to help me compensate. So far this fall I've managed to quell the cravings.
Life should NOT be a journey to the grave with the intention of arriving safely in an attractive and well preserved body, but rather to skid in sideways, champagne in one hand, strawberries in the other, body thoroughly used up, totally worn out and screaming: "Yeah Baby! What a Ride!"