You must learn that with every thought or emotion there is a reaction. This response can either energize you or decrease your life force. For example, when you have a negative thought or negative emotion: 

What happens in your body  

Brain: Negative thoughts or emotions cause the electricity of the brain to change. 

Changes in brain affects meridian: Due to the change of the brain electricity, the meridian energy changes. 

As you know that meidian and organs are connected so 

Organ: The organs connected with the meridian are not properly nourished with vital energy and disease develops. 

Which affect Chakras: The astral energy feedback changes in the chakra due to the bad thought or emotion. This thought or emotion has less vitality as it is out of the cosmic tune. A block in the chakra occurs. 

Aura: Negative thinking drains away the energy of the aura. The colors become dull and the auric protection shield weaker. Negativity from the outside can pour in. 

Law of Resonance: When negative thoughts or emotions are radiated to the environment, all thoughts or emotions on that morphogenetic field will be attracted. The negativity becomes stronger and happens more often. 

Negative thoughts or emotions are against the Godly plan of loving. Bad life conditions will be attracted.