The answer to this question depends on what we would call insanity. Actually, insanity is a complex reversible mental disorder, and, as a rule, we understand it as a state close to the loss of adequacy and even competence. To this degree, it is difficult to be afraid. There are phobias, which are in fact temporary madness (at moments of panic we actually "lose mind", we stop controlling ourselves), but the root cause of this illness, as a rule, is not fear, but neglected internal conflicts and problems. The closest thing to insanity caused by fears are manias and compulsions. For example, persecution mania or fear of death. These are diseases based on fright, which, due to a number of psychological reasons and external circumstances, has gained strength and transformed into such a problem. By the way, American psychiatrists once calculated and found that the most common reason to go insane is the fear of going insane.