Feelings

I think this may be coherent: feelings are electro-chemical responses to the environment. Unlike other events akin, they'll have a more direct endocrine effect in our bodies.

Sadness is a direct correlate of happiness. Whatever causes happiness, it starts an allocation of resources to engage the source (people "perk up" when they're happy). Sadness is the immediate depression of such allocation together with the warning that it could leave you in a deprived state if the allocation is missmanaged or constantly repressed.

Wise as your body is, we are not going to die because we keep engaging sources of happiness, not matter how unfruitful they turn out to be. I'd go a step forward and claim that the constant allocation of resources doesn't even have to have a source. As demanding as it may be for our bodies, we can take it.

As Wittgenstein said, the only moral command could be, be happy!