Top five regrets of the dying

There is definitely a relationship between stress and health. Resentment, especially carried over a lifetime, can be pretty mentally taxing and stressful.

It is in fact possible and is recognized as mental illness, for example take a look at this: http://en.wikipedia.org/wiki/Hwabyeong

Yes, look at Abe Lincoln before and after grieving the death of a girl he knew.

It is very possible to develop all sorts of diseases from cognitive stress (especially chronic long term).

Cognitive processes have a lot of influence on a wide range of physiological processes, including a high potential in causing oxidative stress, depleting your anti-inflammatories, messing with your mitochondria; it's a long list [1]

That's why cognitive-behavioral therapies are thriving so much at the moment, getting to terms with your cognitive processes has a *huge influence on your physical well-being.

[1] https://scholar.google.com/scholar?q=chronic+stress+dysfunct...