Everyone possesses both functions, but according to Jung, one always dominates. If you primarily rely on logic and objective analysis (Thinking),your capacity for subjective, value-based judgment (Feeling) is typically less developed — though it still shapes your responses in subtle ways.
Jung believed that the innate type remains stable. However, through the process of "individuation," a person learns to acknowledge and develop their weaker functions. While this may look like a change of type, it is actually the achievement of psychological maturity and balance.
There is no direct link, but long-term suppression of your natural inclinations (e.g., an introvert forced into a highly social environment) leads to chronic stress and exhaustion, which can contribute to stress-related physical symptoms.