When you have negative thoughts on a regular basis there is a good chance that the fight or flight reaction will also be triggered more often. Over time the body will suffer from continually being brought to such a high alert. You can become mentally and physically exhausted and your immune system is compromised. You are more likely to have digestive problems and suffer from poor sleep. This leads to chronic stress or burn out. At this point one is vulnerable to more serious mental and psychological illness.
When you are mentally and physically exhausted from chronic stress, your body becomes tense and your heart and mind contract. In attempting to deal with chronic stress you may close down emotionally and your perspective may become narrower. Eventually you go into survival mode. You can become more fearful and act less kindly towards yourself and others. The result is a feeling of being disconnected. Feeling separate and alone is the most damaging aspect of stress. It leaves you feeling the need to fend for yourselves. You can experience yourself as acting out of character and not feeling your normal self.