> This is kind of a random theory from a snippets of past thoughts I've had, but sometimes, when happiness is scarce, any happiness you do find is counterbalanced by the fear that it will be fleeting and soon gone. But that's just the first thing I thought of, and it may very well be way off here. ;)

That totally makes sense as a possibility. Next time this happens I am going to try to see if this type of thing is going on in the back of my mind.