Hello, Since how long has this been happening? What measures have you taken yet to handle the situation? The problem is common and needs immediate Psyhciatric and Psychotherapeutic help.

Please understand that the human mind is like a monkey. It is always restless and gets into problems. Everybody gets negative thoughts; there is no exception. Ignoring these thoughts is the only way out. How to ignore them is an art which you should learn through the practice of pranayama, yoga and meditation. But if you constantly have the same negative thought, it might suggest that you have Obsessive traits(if not an obsessive compulsive disorder). Whether it requires treatment can be decided by a psychiatrist only when he can interview you in person. Treatment will also give you relief from your sleep problem.