What is typically the root cause of a patient’s negative or hostile attitude?

It's hard to narrow it down to one root, there are many that can suppress feelings and make a patient negative, or even hostile. 

their physical health, mental health, family structure, relationships with others, work/school environment, societal or socioeconomic factors. individual traits, their surroundings, etc. 

Typically, the root cause is the current condition the patient is in such as the stress factor which is the cause. For example, the patient may be experiencing a mental or emotional crisis that can be a direct result from his/her living, health, mental, emotional or psychological condition. A negative or hostile attitude, not always, but often stems from any, some or all of the aforementioned factors. Some do not know how to cope with their conditions well, so negative or hostile attitudes are a sign of inability to cope or understand their current condition.

Make a decision because you before you make a decision you have to know what it’s about and do reasearch