The Syracusan tyrant Dionysius was ever fearful of assassination. He allowed no one to trim his beard with a razor, so wary of having his throat slit was he. He trained his young daughters to trim his beard, and as they grew older, had them use heated walnut shells to singe off the hairs of his beard, and when they found husbands, he ceased even this. He slept surrounded by a moat, which could only be crossed by a plank, which he kept on his side of the ditch. Is it any wonder that he saw his position as a sword forever held above his head, suspended by a single hair?
The only one I can think of in the same category of paranoia as Dionysius is Herod the Great. Herod was so afraid of being overthrown and assassinated. He had his brother executed, most of his children killed and any and all for plotting against him.
Augustus once commented of Herod that he would rather be his pig than his son. Considering Herod kept kosher, you’d probably be safer.