Why is Oedipus frightened by the information given by Jocasta?

Oedipus is frightened by Jocasta's information because of Polybus and Merope, his father and mother and king and queen of Corinth. A drunken man, he says, once accused him of being a bastard at a feast - and he confronted his parents with this to no avail. Eventually he went to an oracle, which did not tell him of his parentage, but warned him he would sleep with his mother and murder his father. Oedipus then fled Corinth, and at a crossroads, fell into an argument with an old man in a coach. Oedipus “struck him backwards from the car” (811) and killed him. Oedipus now fears that he has killed Laius, his father, and married Jocasta, his mother, but waits for the herdsman to arrive. Oedipus hopes that the herdsman will say that many people killed Laius - for he alone killed the man at the crossroads.