I have gone through a similar experience to the above. Simply put, i experience severe anxiety and panic attacks. Feelings of euphoria and depression are frequent occurances and tend to happen at specific times of the day. Because, the chemicals within your brain are out of balance, your "Fight or flight instinct" is damaged, THC also alters communication between neutrons within your brain. These affects induce, paranoia, depression, and anxiety. And if not understood properly can lead to halllucinationa and other symptoms of psychosis.
Drugs offer a fair treatment. However, personally, equilibrium within the brain is delicate and the side-affects of such drugs may prove detrimental to your mental well-being.
To overcome this, you have to alter your outlook on life. Stop trying to rationalize your depression, anxiety or paranoia. Your mind feeds on your own rationalization and enhances these feelings.
Accept that you have a problem mentally and adjust the way you think about things. Always bring yourself into the present and simplyfy your environment. Keep yourself busy with positive things.
Eventually these feelings of anxiety, paranoia and depression will sub-side. With time, they WILL dissapear. Remember that