Nearly everyone has negative thoughts sometimes. Negative thoughts often occur before negative emotions*. It's important to regularly monitor, and deal with a negative internal monologue (self talk), or mental process, such as disturbing thoughts, images, impulses, etc., by the process of (a): recognising it, and (b): challenging it immediately. Use the "Technique For Re-Programming Negative Thoughts" - When you notice something negative, such as: "I can't do this/ am never going to get over this!" or: "Why am I always so useless/such a loser?" or even an image, emotion, or a memory; recognise that it is being generated from the negative part of your mind.
After identifying and labelling it, visualise a large, red, flashing, "STOP!" sign, and/or possibly a stern faced person wagging an index finger at you in a negative manner, then say to yourself as forcefully as you can, even aloud in a big voice, if alone: "I know this tactic: GO AWAY FOR A WHILE !!!" You may want to use either: "ruse", "ploy", "game", or "trick". In the case of an image, visualise a large "STOP" sign, or your preferred version.
Some people go so far as to keep a wide rubber band in their pocket, then put it around their wrist, when they catch themselves backsliding, stretch and release it, as a method of reprogramming their mind sooner, but I don't regard it as being strictly necessary. Remember to remove it, afterwards, if you use this method. Try replacing a negative thought with a positive affirmation of your choice, like: "I am a unique individual, with my own set of skills, and good points", or "I may not be perfect, but I'm doing the best I can, right now", or "I choose to be more positive". Recommended reading: Positivity: Groundbreaking Research Reveals How to Embrace the Hidden Strength of Positive Emotions, Overcome Negativity, and Thrive by Barbara Fredrickson, & Negaholics: How to Overcome Negativity and Turn Your Life Around by Chérie Carter-Scott, from your bookstore, or amazon.com
"Even if we have some vague idea that we are not our feelings or our thoughts, when we are experiencing painful feelings or painful thoughts, we believe we have to feel them or think them just because of the fact that they are occurring to us. But painful feelings can be indirectly controlled by physical action, and changing our present thoughts for different thoughts (since feeling occurs as a result of thinking.) Painful thoughts can be directly controlled by choosing replacement thoughts for the ones that are troubling us. Sure, it takes some practice to change a long habit of suffering. But it can be done. Of course it can't be done if we choose to believe that it can't be done. But, since the choice is ours, why not choose to believe it can be done, and do it?" Read: Change How You Feel by Changing the Way You Think by Dennis Greenberger and Christine Padesky, & Change Your Thinking by Sarah Edelman, & "Feeling Good." The New Mood Therapy. Harper Collins.1999. ( updated sequel to his US bestseller about treating depression & anxiety; very comprehensive), by David D. Burns, M.D.
Hypnosis is merely a heightened state of suggestibility, in which you are better able to communicate with your subconscious mind; view http://myfavoriteinterests.com/hypnosis/ about what it is, and isn't. 85% of people are suggestible to some degree; 15% - 20% highly so, and 15% - 20% aren't much at all, so you could either preferably seek professional hypnotherapy, or, if not an option, hypnosisdownloads.com has one about stopping negative thoughts.
"I cannot always control what goes on outside. But I can always control what goes on inside" - Dr. Wayne Dyer*.