Why is sanity a recurring theme in Haiyore Nyaruko-san? In several episodes, sanity is discussed by the characters. There is even a sunscreen to protect sanity from UV rays.

What is the purpose of sanity in the anime? Why is it a recurring theme?
Haiyore Nyaruko-san is based on Lovecraft's mythos, which includes the concept of Eldritch abomination. It has been said that when one gazes at or even think about such abominations, they will slowly lose their sanity as they are beyond comprehension. Many of the characters in his works regularly succumbs to insanity, slowly but surely. It is a common theme that these characters are vulnerable and fragile, keeping up with his other theme of humanity being insignificant when compared to the grand scheme of the universe. 

It's a recurring theme in the anime because it is based on a work that has the loss of sanity as a recurring theme. 

It should also be noted that Nyaruko is a satire of the mythos. Many of the tropes and themes in the anime are greatly exaggerated because of this. They are hyperbolic to achieve a comedic effect.

As for the Sanity points, it may refer to the many board games that has a Lovecraftian theme. Board games such as Betrayal at House on the Hill would be just one example, as it uses sanity checks as part of its gameplay.

Source


http://en.wikipedia.org/wiki/Lovecraftian_horror
http://en.wikipedia.org/wiki/Nyaruko:_Crawling_with_Love