How much of thought or feeling is consciously derived vs. derived from a persons environment? Humans don't 'create' the world around them - the world around them gives inputs for their minds (not the opposite).
Depending on the input (or the situation) a human mind could interpret the inputs in different ways. They could cause the person to feel emotions that they didn't expect to feel or that they didn't ask for. Their mind also biases the information that it thinks. It seems like the mind could structure new ways of thinking about things and how the feelings are generated when thinking about those things by practicing new ways of thinking.
Old habits die hard; however. When thinking about things feelings are automatically triggered - and these feelings have real sources in the world (which is perhaps why it is hard to change how they make you feel).
It probably depends if the thinking is context independent or context dependent - for instance if you are thinking in a different environment or have different emotions when you do the thinking. The context I am talking about here must be more complicated than 'background' feelings because the content is highly informational. There are a only a few background feelings someone could experience however there are many more ways of feeling in your mind if you combine the feelings with thoughts or specific situations.