Act 1, Sc. 4, lines 82-89: What does Hamlet's behavior here make Horatio fear?

Marcellus: You shall not go, my lord.

[They hold back Hamlet]

Hamlet: Hold off your hands.

Horatio: Be ruled. You shall not go.

Hamlet: My fate cries out And makes each pretty arture in this body As hardy as the Neamean lion's nerve. Still am I called. Unhand me, gentlemen. By heaven, I'll make a ghost of him that lets me! I say, away!---Go on. I'll follow thee.

[Ghost and Hamlet exit]

Horatio: He waxes desperate with imagination.