Haha...I can relate to being a worrywart! I poked around at the bottom and it seems dry--the rocks at the bottom are technically decorative polished stones, so liquid slides right off them.
My running theory is that he's bummed out that the sun hasn't showed up since it's winter here in the midwest. He's made it through 4 winters here, so maybe his spines will regain their vigor when the sun pokes out again! Unfortunately I've always lived in an apartment, so my cactus cannot sit outside. I can get them right up to the window at best.
I'll closely watch how the cactus react to the upcoming summer...if they still look gloomy, I can invest in a heat lamp!
