Bad Health Reduces Function Performance
When in bad health, certain cognitive functions may be perceived to have subpar performance, so much so that they may be interpreted as having a low priority in the stack. For example, a long-term sleep deprivation could result in weakened cognitive abilities, which would in turn lower the apparent position of Ti (by reducing its analytic and problem-solving capabilities) and Te (by crippling executive functions of the frontal cortex) in the function stack.
Bad Health Prioritizes Certain Functions
Certain mental disorders or bad circumstances in life may also boost functions. For one, Fi can typically rise in the function stack when the subject has a depressive mood. This is why it may be unwise to type a person when he/she is in an untypical mood or has a mental disorder. It is also commonly known that the MBTI function stack reorders under stress, making the lesser-used functions rise to the top and increasing the likelihood of mistyping.