My last clue, regarding Noodles Vague Question, will require a little lateral thinking.

[Dujon]One of my sister in-laws has been going through it all of her life. she recovered for a short while a couple of years ago but we have noticed that she started back down that path again a few months ago.

There is not more than one of them.
It is not numerical.
It does not involve religion.
It is not unique to humans.
You could possibly pay money to buy some.
It can be seen.
It can be perceived by the senses.
It does involve emotion.
It is not love.
It would not be considered one of the 'arts'.
Is it not generally considered to be a positive thing.
It isn't a colour.
It isn't one of the seven deadly sins.
It couldn't exist without animals or humans.
It elicits an emotional response.
It isn't pain.
It isn't childbirth.
It isn't mortality.
It doesn't, as a rule, cause physical damage.
It is not considered a disease.
It is not a positive thing.
It isn't sex.
It isn't impotence.
It isn't artificial.
It isn't rabies.
It isn't a short lifespan.
It isn't exclusive to humans.
It isn't death.
It isn't obesity [but 'close' said Hux].
It doesn't involve one specific emotion.
It isn't a celebration.
It isn't 'an' emotion.
It isn't crying.
It isn't love.
It isn't depression.
It isn't anorexia nervosa.

OK there seem to be some missing answers, if I've read it right:
Is it an action? [Bob]
Is it dieting? [Darren]
Is it unhappiness? [Chalky]
Is it self-consciousness? [LotUS]
Is it something to do with physical appearance? [Darren]
Phew!