Thanks everyone for your responses! I'm glad I'm not the only one who feels this way (of course, on here I discover I'm never alone).

On this I found so interesting was a Psych Central article just posted yesterday, 27 Twisted Thoughts that Block Happiness.

The first two points were:

1. When I am happy, bad news is coming, because happiness can’t last.

2. When I am happy, I am setting myself up for disappointment.

Wow, we are most certainly not the only ones!