Go and meet a psychologist and understand the basis of fear by sharing your emotions and happenings in your life. U might an answer.

You seem to have developed phobic anxiety about darkness and night. This needs to addressed like any other phobic anxiety. Normally working with a therapist would give you a better structure and confidence to use gradual systematicl desensitisation techniques, which is essentially exposing you to higher anxiety provoking situations gradually whilst helping to overcome them using specific cognitive techniques and relaxation. Medicine may be necessary as it is affecting your sleep too. Also, need to rule out any other underlying factors contributing to this. Meet a psychiatrist to plan this treatment in a systematic way. Regards