DH here: my DW never initiates, so this is a kind of a theoretical question, but I can see turning her down in cases of illness or rather extreme fatigue. Most men are up for sex 95%+ of the time so this is quite normal. In the scenario you posit, he wasn’t horny at that moment, but the mere mention of sex changed that relatively quickly. This too is normal. Sex is an ever present desire for most men in ways most women don’t understand. Low T can change that a lot though, as can SSRIs