Tolerance can in fact cause an overdose, because the greater tolerance you can get the more of a certain substance your body will need eventually leading your body to take more than it can handle leading to overdose and death.
Pessimism would be the term. A pessimist often focuses on the most dangerous or bad outcomes in life, letting it cloud their happiness and judgement occasionally(being a mindset/lifestyle and all).
Milk, yogurt, most dairy can be rich source of calcium